Why So Many Units?...

[Lasse Langwadt Christensen]

tirsdag den 21. juli 2020 kl. 20.53.55 UTC+2 skrev John Larkin:

On Mon, 20 Jul 2020 18:14:10 -0700 (PDT), George Herold
ggherold@gmail.com> wrote:

On Monday, July 20, 2020 at 5:41:38 PM UTC-4, DemonicTubes wrote:
On Monday, July 20, 2020 at 12:23:22 AM UTC-6, Ricketty C wrote:
I thought the point of SI was to unify the use of units so everyone could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Torque units are equally frustrating. According to SI it is supposed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

We are also a chemistry lab. Concentration units...grrr! This is worse. Units can be mass-per-volume or number-per-volume. Depending on the industry we are serving, the preferred units are different. It gets a bit obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling to find the molecular weight of this that and the other thing. And that is just the metric units!

Always makes me chuckle when somebody says Americans don\'t understand metric. We understand metric just fine, we just also happen to know a bunch of other units and know how to convert between them.

As far as I\'m concerned, getting the units right is part of the job.
My \'learning units\' story involves making an impedance line for
a helium flow cryostat. I made a factor of ten error in the pressure
(Pascals to atm. IIRC) and made the impedance x10 greater than necessary
(or wanted!)
Since the flow impedance \'recipe\' involved cramming some wire
into a thin SS tube. I wasted a lot of time making the wrong
value of flow impedance. And ~$100 1980 dollars (20 liters)
of liquid helium, discovering my mistake.
I was younger then :^)

George H.
I like ft-lbs when torquing head gaskets and such.

Here\'s my little units program.

https://www.dropbox.com/s/64rg7ko4rc7hhw7/U.zip?dl=0

I could add pressure, but we rarely deal with that.

or just type it into google, the google calculator handle most units

 

[Lasse Langwadt Christensen]

tirsdag den 21. juli 2020 kl. 20.53.55 UTC+2 skrev John Larkin:

On Mon, 20 Jul 2020 18:14:10 -0700 (PDT), George Herold
ggherold@gmail.com> wrote:

On Monday, July 20, 2020 at 5:41:38 PM UTC-4, DemonicTubes wrote:
On Monday, July 20, 2020 at 12:23:22 AM UTC-6, Ricketty C wrote:
I thought the point of SI was to unify the use of units so everyone could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Torque units are equally frustrating. According to SI it is supposed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

We are also a chemistry lab. Concentration units...grrr! This is worse. Units can be mass-per-volume or number-per-volume. Depending on the industry we are serving, the preferred units are different. It gets a bit obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling to find the molecular weight of this that and the other thing. And that is just the metric units!

Always makes me chuckle when somebody says Americans don\'t understand metric. We understand metric just fine, we just also happen to know a bunch of other units and know how to convert between them.

As far as I\'m concerned, getting the units right is part of the job.
My \'learning units\' story involves making an impedance line for
a helium flow cryostat. I made a factor of ten error in the pressure
(Pascals to atm. IIRC) and made the impedance x10 greater than necessary
(or wanted!)
Since the flow impedance \'recipe\' involved cramming some wire
into a thin SS tube. I wasted a lot of time making the wrong
value of flow impedance. And ~$100 1980 dollars (20 liters)
of liquid helium, discovering my mistake.
I was younger then :^)

George H.
I like ft-lbs when torquing head gaskets and such.

Here\'s my little units program.

https://www.dropbox.com/s/64rg7ko4rc7hhw7/U.zip?dl=0

I could add pressure, but we rarely deal with that.

or just type it into google, the google calculator handle most units

 

[Ricketty C]

On Tuesday, July 21, 2020 at 11:52:51 AM UTC-4, Lasse Langwadt Christensen wrote:

tirsdag den 21. juli 2020 kl. 17.18.42 UTC+2 skrev Ricketty C:
On Tuesday, July 21, 2020 at 3:47:40 AM UTC-4, Clifford Heath wrote:
On 20/7/20 8:00 pm, Piotr Wyderski wrote:
Ricketty C wrote:

I thought the point of SI was to unify the use of units so everyone
could speak the same language?

People cannot even agree what a ton is.

WTF?!  Why have multiple units like this?

Do you express fuel consumption of cars in square meters, as it should
have always been? This is the cross-section area of the virtual stream
of fuel running along your car when you are driving. Self-normalised,
doesn\'t need any \"per 100km\".

It\'s the cross-section area of a long thread of fuel that you car can
use to follow without losing speed. Ours does better than 0.1mm^2 only
on the highway, approximately a 0.25mm diameter thread of fuel. That
doesn\'t seem like much.

For electric cars, the measure is newtons, the force required to
maintain velocity against drag. Even for gasoline cars, that would be
more instructive, with a separate efficiency measure for the engine.

Clifford Heath.

Newton is not useful since it will vary hugely over speed and only be useful to compare cars directly while saying nothing about what you really care about, cost.

What really matters is $/mile or €/mile, etc. Since the cost of electricity varies widely the energy per mile is useful as joules/mile or more commonly, even if not SI, kWh/mi. Of course these numbers will be related to driving patterns, but not the huge, direct impact that newtons suffer, just the same smaller effect we are used to with MPG.

A measure that would be similar to your newton number would simply be kW. This will relate more to useful units that can be used to find energy consumption and cost. I love mashing the accelerator and watching the kW meter run up to 400 in my car.

Oh yeah, my car needs 1.25 amps at 240 V to run on the highway at 60 MPH (97 kph) which will require a wire of about 20 gauge which is about 0.5 mm^2 cross section, 0.8 mm diameter.


that\'s a way off, 300W is what a decent cyclist can do

a car doing 100km/h will take something like 10-15kW

Tesla3, 75kWh battery, 500km range

75kWh/15kW = 5 hours, 5 hours * 100km/h = 500km

Yes, you are right. It is 300 WH/mi I was thinking of for my X. The 3 gets more like 250 or even 200 WH/mi.

So I guess I\'m going to need a bigger wire!

Oddly enough, both the consumption and vampire drain have improved as of late. The consumption could be helped by the warm weather, but I\'ve had the car for two years now and the improvement actually was first noticed in the early spring when it was still cold. I know they do continual updates and maybe they\'ve improved the efficiency of the system? It used to be 333 Wh/mi was a goal and 300 Wh/mi was a really good drive. Now I can expect 333 Wh/mi and often get 300 Wh/mi and even lower. It\'s kinda like those gadgets you add to your car to improve the mileage by 10-20-30%!!! The battery is down around 5-6% of original capacity, so improvements in range are welcome.

One thing I keep reminding myself of is that the Supercharging is free to me as long as I own the car. That alone is worth $20,000. Nice!

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Tuesday, July 21, 2020 at 11:52:51 AM UTC-4, Lasse Langwadt Christensen wrote:

tirsdag den 21. juli 2020 kl. 17.18.42 UTC+2 skrev Ricketty C:
On Tuesday, July 21, 2020 at 3:47:40 AM UTC-4, Clifford Heath wrote:
On 20/7/20 8:00 pm, Piotr Wyderski wrote:
Ricketty C wrote:

I thought the point of SI was to unify the use of units so everyone
could speak the same language?

People cannot even agree what a ton is.

WTF?!  Why have multiple units like this?

Do you express fuel consumption of cars in square meters, as it should
have always been? This is the cross-section area of the virtual stream
of fuel running along your car when you are driving. Self-normalised,
doesn\'t need any \"per 100km\".

It\'s the cross-section area of a long thread of fuel that you car can
use to follow without losing speed. Ours does better than 0.1mm^2 only
on the highway, approximately a 0.25mm diameter thread of fuel. That
doesn\'t seem like much.

For electric cars, the measure is newtons, the force required to
maintain velocity against drag. Even for gasoline cars, that would be
more instructive, with a separate efficiency measure for the engine.

Clifford Heath.

Newton is not useful since it will vary hugely over speed and only be useful to compare cars directly while saying nothing about what you really care about, cost.

What really matters is $/mile or €/mile, etc. Since the cost of electricity varies widely the energy per mile is useful as joules/mile or more commonly, even if not SI, kWh/mi. Of course these numbers will be related to driving patterns, but not the huge, direct impact that newtons suffer, just the same smaller effect we are used to with MPG.

A measure that would be similar to your newton number would simply be kW. This will relate more to useful units that can be used to find energy consumption and cost. I love mashing the accelerator and watching the kW meter run up to 400 in my car.

Oh yeah, my car needs 1.25 amps at 240 V to run on the highway at 60 MPH (97 kph) which will require a wire of about 20 gauge which is about 0.5 mm^2 cross section, 0.8 mm diameter.


that\'s a way off, 300W is what a decent cyclist can do

a car doing 100km/h will take something like 10-15kW

Tesla3, 75kWh battery, 500km range

75kWh/15kW = 5 hours, 5 hours * 100km/h = 500km

Yes, you are right. It is 300 WH/mi I was thinking of for my X. The 3 gets more like 250 or even 200 WH/mi.

So I guess I\'m going to need a bigger wire!

Oddly enough, both the consumption and vampire drain have improved as of late. The consumption could be helped by the warm weather, but I\'ve had the car for two years now and the improvement actually was first noticed in the early spring when it was still cold. I know they do continual updates and maybe they\'ve improved the efficiency of the system? It used to be 333 Wh/mi was a goal and 300 Wh/mi was a really good drive. Now I can expect 333 Wh/mi and often get 300 Wh/mi and even lower. It\'s kinda like those gadgets you add to your car to improve the mileage by 10-20-30%!!! The battery is down around 5-6% of original capacity, so improvements in range are welcome.

One thing I keep reminding myself of is that the Supercharging is free to me as long as I own the car. That alone is worth $20,000. Nice!

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Tuesday, July 21, 2020 at 11:52:51 AM UTC-4, Lasse Langwadt Christensen wrote:

tirsdag den 21. juli 2020 kl. 17.18.42 UTC+2 skrev Ricketty C:
On Tuesday, July 21, 2020 at 3:47:40 AM UTC-4, Clifford Heath wrote:
On 20/7/20 8:00 pm, Piotr Wyderski wrote:
Ricketty C wrote:

I thought the point of SI was to unify the use of units so everyone
could speak the same language?

People cannot even agree what a ton is.

WTF?!  Why have multiple units like this?

Do you express fuel consumption of cars in square meters, as it should
have always been? This is the cross-section area of the virtual stream
of fuel running along your car when you are driving. Self-normalised,
doesn\'t need any \"per 100km\".

It\'s the cross-section area of a long thread of fuel that you car can
use to follow without losing speed. Ours does better than 0.1mm^2 only
on the highway, approximately a 0.25mm diameter thread of fuel. That
doesn\'t seem like much.

For electric cars, the measure is newtons, the force required to
maintain velocity against drag. Even for gasoline cars, that would be
more instructive, with a separate efficiency measure for the engine.

Clifford Heath.

Newton is not useful since it will vary hugely over speed and only be useful to compare cars directly while saying nothing about what you really care about, cost.

What really matters is $/mile or €/mile, etc. Since the cost of electricity varies widely the energy per mile is useful as joules/mile or more commonly, even if not SI, kWh/mi. Of course these numbers will be related to driving patterns, but not the huge, direct impact that newtons suffer, just the same smaller effect we are used to with MPG.

A measure that would be similar to your newton number would simply be kW. This will relate more to useful units that can be used to find energy consumption and cost. I love mashing the accelerator and watching the kW meter run up to 400 in my car.

Oh yeah, my car needs 1.25 amps at 240 V to run on the highway at 60 MPH (97 kph) which will require a wire of about 20 gauge which is about 0.5 mm^2 cross section, 0.8 mm diameter.


that\'s a way off, 300W is what a decent cyclist can do

a car doing 100km/h will take something like 10-15kW

Tesla3, 75kWh battery, 500km range

75kWh/15kW = 5 hours, 5 hours * 100km/h = 500km

Yes, you are right. It is 300 WH/mi I was thinking of for my X. The 3 gets more like 250 or even 200 WH/mi.

So I guess I\'m going to need a bigger wire!

Oddly enough, both the consumption and vampire drain have improved as of late. The consumption could be helped by the warm weather, but I\'ve had the car for two years now and the improvement actually was first noticed in the early spring when it was still cold. I know they do continual updates and maybe they\'ve improved the efficiency of the system? It used to be 333 Wh/mi was a goal and 300 Wh/mi was a really good drive. Now I can expect 333 Wh/mi and often get 300 Wh/mi and even lower. It\'s kinda like those gadgets you add to your car to improve the mileage by 10-20-30%!!! The battery is down around 5-6% of original capacity, so improvements in range are welcome.

One thing I keep reminding myself of is that the Supercharging is free to me as long as I own the car. That alone is worth $20,000. Nice!

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 4:14:56 AM UTC-4, Mikko OH2HVJ wrote:

Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

And then there are absolute and gauge pressures, which you also need to
take into account with ventilators and code!

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

Fully agreed. But I find that fight one I can\'t win and thus propose
minimally error prone common units. Of course sometimes the 2% error can
make a difference..

Yeah, I\'m trying to put together a document that starts with units of measurement of several sensors and document the path to the ADC reading so we know exactly what our range needs to be and what we achieve. People keep getting in the way of this by mucking with the units but also saying we should enter the full range of a sensor instead of just the range we are required to measure. Meanwhile we have a problem with adequate resolution at the low end.

Design by committee is not always fun.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 4:14:56 AM UTC-4, Mikko OH2HVJ wrote:

Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

And then there are absolute and gauge pressures, which you also need to
take into account with ventilators and code!

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

Fully agreed. But I find that fight one I can\'t win and thus propose
minimally error prone common units. Of course sometimes the 2% error can
make a difference..

Yeah, I\'m trying to put together a document that starts with units of measurement of several sensors and document the path to the ADC reading so we know exactly what our range needs to be and what we achieve. People keep getting in the way of this by mucking with the units but also saying we should enter the full range of a sensor instead of just the range we are required to measure. Meanwhile we have a problem with adequate resolution at the low end.

Design by committee is not always fun.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 4:39:44 AM UTC-4, Martin Brown wrote:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

It is a custom and practice thing. mmHg is still used for blood pressure
since conversion to pascals resulted in too many errors. Mercury
manometers have not been used to do the measurement for many decades.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

I don\'t recall ever seeing mmH2O or cmH2O before.

mBar and Torr persist in my field and there are still good textbooks in
cgs units so you have to be reasonably adept at living with a few orders
of magnitude here and there.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

Or mass flow controllers which are calibrated by amount delivered.

This is about a flow measurement which in the commercial unit is specified as SLM, standard liters per minute. We seem to prefer the unit of ml/s.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 4:39:44 AM UTC-4, Martin Brown wrote:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

It is a custom and practice thing. mmHg is still used for blood pressure
since conversion to pascals resulted in too many errors. Mercury
manometers have not been used to do the measurement for many decades.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

I don\'t recall ever seeing mmH2O or cmH2O before.

mBar and Torr persist in my field and there are still good textbooks in
cgs units so you have to be reasonably adept at living with a few orders
of magnitude here and there.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

Or mass flow controllers which are calibrated by amount delivered.

This is about a flow measurement which in the commercial unit is specified as SLM, standard liters per minute. We seem to prefer the unit of ml/s.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 4:39:44 AM UTC-4, Martin Brown wrote:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

It is a custom and practice thing. mmHg is still used for blood pressure
since conversion to pascals resulted in too many errors. Mercury
manometers have not been used to do the measurement for many decades.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

I don\'t recall ever seeing mmH2O or cmH2O before.

mBar and Torr persist in my field and there are still good textbooks in
cgs units so you have to be reasonably adept at living with a few orders
of magnitude here and there.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

Or mass flow controllers which are calibrated by amount delivered.

This is about a flow measurement which in the commercial unit is specified as SLM, standard liters per minute. We seem to prefer the unit of ml/s.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 6:00:39 AM UTC-4, Piotr Wyderski wrote:

Ricketty C wrote:

I thought the point of SI was to unify the use of units so everyone could speak the same language?

People cannot even agree what a ton is.

WTF?! Why have multiple units like this?

Do you express fuel consumption of cars in square meters, as it should
have always been? This is the cross-section area of the virtual stream
of fuel running along your car when you are driving. Self-normalised,
doesn\'t need any \"per 100km\".

But varies with the temperature of the fuel, so will need to be @25°C still. Sm^2... standard square meters.

Mechanical horsepower is fun as well. Maybe we should consider
specifying the power of SMPSes that way.

I think it\'s 1.3 HP per kW, no? That\'s an easy one if everyone agrees on what a HP is. I\'m happy rating my car in kW.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 6:00:39 AM UTC-4, Piotr Wyderski wrote:

Ricketty C wrote:

I thought the point of SI was to unify the use of units so everyone could speak the same language?

People cannot even agree what a ton is.

WTF?! Why have multiple units like this?

Do you express fuel consumption of cars in square meters, as it should
have always been? This is the cross-section area of the virtual stream
of fuel running along your car when you are driving. Self-normalised,
doesn\'t need any \"per 100km\".

But varies with the temperature of the fuel, so will need to be @25°C still. Sm^2... standard square meters.

Mechanical horsepower is fun as well. Maybe we should consider
specifying the power of SMPSes that way.

I think it\'s 1.3 HP per kW, no? That\'s an easy one if everyone agrees on what a HP is. I\'m happy rating my car in kW.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 6:00:39 AM UTC-4, Piotr Wyderski wrote:

Ricketty C wrote:

I thought the point of SI was to unify the use of units so everyone could speak the same language?

People cannot even agree what a ton is.

WTF?! Why have multiple units like this?

Do you express fuel consumption of cars in square meters, as it should
have always been? This is the cross-section area of the virtual stream
of fuel running along your car when you are driving. Self-normalised,
doesn\'t need any \"per 100km\".

But varies with the temperature of the fuel, so will need to be @25°C still. Sm^2... standard square meters.

Mechanical horsepower is fun as well. Maybe we should consider
specifying the power of SMPSes that way.

I think it\'s 1.3 HP per kW, no? That\'s an easy one if everyone agrees on what a HP is. I\'m happy rating my car in kW.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 11:35:39 AM UTC-4, Tauno Voipio wrote:

On 20.7.20 17.09, jlarkin@highlandsniptechnology.com wrote:
On Mon, 20 Jul 2020 09:39:39 +0100, Martin Brown
\'\'\'newspam\'\'\'@nezumi.demon.co.uk> wrote:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

It is a custom and practice thing. mmHg is still used for blood pressure
since conversion to pascals resulted in too many errors. Mercury
manometers have not been used to do the measurement for many decades.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

I don\'t recall ever seeing mmH2O or cmH2O before.

mBar and Torr persist in my field and there are still good textbooks in
cgs units so you have to be reasonably adept at living with a few orders
of magnitude here and there.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

Or mass flow controllers which are calibrated by amount delivered.

Around here, domestic gas pressure is measured in inches of water, or
just \"inches\", roughly six.

It used to be distributed at that pressure, but now it\'s some higher
pressure with a regulator at each house.

\"Inch\" is a funny sounding word.


American aviation is using inches of mercury for air pressure and
piston engine mainfold pressure. Other pressures are in psi, pounds
per square inch.

The inch measure of pressure was from the method of measuring it, with a column of water or mercury. That\'s easy to understand, but very awkward for the exact reason SI units were developed, to get rid of most conversion coefficients.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 11:35:39 AM UTC-4, Tauno Voipio wrote:

On 20.7.20 17.09, jlarkin@highlandsniptechnology.com wrote:
On Mon, 20 Jul 2020 09:39:39 +0100, Martin Brown
\'\'\'newspam\'\'\'@nezumi.demon.co.uk> wrote:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

It is a custom and practice thing. mmHg is still used for blood pressure
since conversion to pascals resulted in too many errors. Mercury
manometers have not been used to do the measurement for many decades.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

I don\'t recall ever seeing mmH2O or cmH2O before.

mBar and Torr persist in my field and there are still good textbooks in
cgs units so you have to be reasonably adept at living with a few orders
of magnitude here and there.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

Or mass flow controllers which are calibrated by amount delivered.

Around here, domestic gas pressure is measured in inches of water, or
just \"inches\", roughly six.

It used to be distributed at that pressure, but now it\'s some higher
pressure with a regulator at each house.

\"Inch\" is a funny sounding word.


American aviation is using inches of mercury for air pressure and
piston engine mainfold pressure. Other pressures are in psi, pounds
per square inch.

The inch measure of pressure was from the method of measuring it, with a column of water or mercury. That\'s easy to understand, but very awkward for the exact reason SI units were developed, to get rid of most conversion coefficients.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 11:35:39 AM UTC-4, Tauno Voipio wrote:

On 20.7.20 17.09, jlarkin@highlandsniptechnology.com wrote:
On Mon, 20 Jul 2020 09:39:39 +0100, Martin Brown
\'\'\'newspam\'\'\'@nezumi.demon.co.uk> wrote:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
Ricketty C <gnuarm.deletethisbit@gmail.com> writes:

I thought the point of SI was to unify the use of units so everyone
could speak the same language? On this ventilator I am find many ways
of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Historical reasons and being \'understandable\'- the same argument as for
Imperial units.

It is a custom and practice thing. mmHg is still used for blood pressure
since conversion to pascals resulted in too many errors. Mercury
manometers have not been used to do the measurement for many decades.

Out of those only one is part of SI. The medical people are mostly using
cmH2O around here, but that\'s conviniently close enough to 1 hPa /
1 mbar.

I don\'t recall ever seeing mmH2O or cmH2O before.

mBar and Torr persist in my field and there are still good textbooks in
cgs units so you have to be reasonably adept at living with a few orders
of magnitude here and there.

Part of design co-operation should be defining and enforcing the units to
reduce possible mistakes.

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

Gases are compressible and the correct unit should be g/s ;-)

Or mass flow controllers which are calibrated by amount delivered.

Around here, domestic gas pressure is measured in inches of water, or
just \"inches\", roughly six.

It used to be distributed at that pressure, but now it\'s some higher
pressure with a regulator at each house.

\"Inch\" is a funny sounding word.


American aviation is using inches of mercury for air pressure and
piston engine mainfold pressure. Other pressures are in psi, pounds
per square inch.

The inch measure of pressure was from the method of measuring it, with a column of water or mercury. That\'s easy to understand, but very awkward for the exact reason SI units were developed, to get rid of most conversion coefficients.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 6:11:07 PM UTC-4, omni...@gmail.com wrote:

On Monday, July 20, 2020 at 11:41:38 AM UTC-10, DemonicTubes wrote:
On Monday, July 20, 2020 at 12:23:22 AM UTC-6, Ricketty C wrote:
I thought the point of SI was to unify the use of units so everyone could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Torque units are equally frustrating. According to SI it is supposed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

We are also a chemistry lab. Concentration units...grrr! This is worse.. Units can be mass-per-volume or number-per-volume. Depending on the industry we are serving, the preferred units are different. It gets a bit obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling to find the molecular weight of this that and the other thing. And that is just the metric units!

Always makes me chuckle when somebody says Americans don\'t understand metric. We understand metric just fine, we just also happen to know a bunch of other units and know how to convert between them.

One atmosphere of pressure is 101,325 Pascals metric.

Torque is in units of Joules

So does a torque of 1 Nm do 1 joule of work in a radian of rotation?


> The Ohm is events per second.

Got me on that one. How does that work?

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 6:11:07 PM UTC-4, omni...@gmail.com wrote:

On Monday, July 20, 2020 at 11:41:38 AM UTC-10, DemonicTubes wrote:
On Monday, July 20, 2020 at 12:23:22 AM UTC-6, Ricketty C wrote:
I thought the point of SI was to unify the use of units so everyone could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Torque units are equally frustrating. According to SI it is supposed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

We are also a chemistry lab. Concentration units...grrr! This is worse.. Units can be mass-per-volume or number-per-volume. Depending on the industry we are serving, the preferred units are different. It gets a bit obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling to find the molecular weight of this that and the other thing. And that is just the metric units!

Always makes me chuckle when somebody says Americans don\'t understand metric. We understand metric just fine, we just also happen to know a bunch of other units and know how to convert between them.

One atmosphere of pressure is 101,325 Pascals metric.

Torque is in units of Joules

So does a torque of 1 Nm do 1 joule of work in a radian of rotation?


> The Ohm is events per second.

Got me on that one. How does that work?

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Monday, July 20, 2020 at 6:11:07 PM UTC-4, omni...@gmail.com wrote:

On Monday, July 20, 2020 at 11:41:38 AM UTC-10, DemonicTubes wrote:
On Monday, July 20, 2020 at 12:23:22 AM UTC-6, Ricketty C wrote:
I thought the point of SI was to unify the use of units so everyone could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

Pascals
mmH2O
cmH2O
mBar
and another one I didn\'t even recognize. lol

Likewise I\'m finding flow rates indicated as either
ml/s
SLM (standard liters per minute)

WTF?! Why have multiple units like this? This is all in the same field really. People just like to use different units.

Damn them to hell!!!

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Torque units are equally frustrating. According to SI it is supposed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

We are also a chemistry lab. Concentration units...grrr! This is worse.. Units can be mass-per-volume or number-per-volume. Depending on the industry we are serving, the preferred units are different. It gets a bit obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling to find the molecular weight of this that and the other thing. And that is just the metric units!

Always makes me chuckle when somebody says Americans don\'t understand metric. We understand metric just fine, we just also happen to know a bunch of other units and know how to convert between them.

One atmosphere of pressure is 101,325 Pascals metric.

Torque is in units of Joules

So does a torque of 1 Nm do 1 joule of work in a radian of rotation?


> The Ohm is events per second.

Got me on that one. How does that work?

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Clifford Heath]

On 22/7/20 5:28 am, Ricketty C wrote:

On Tuesday, July 21, 2020 at 11:52:51 AM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 21. juli 2020 kl. 17.18.42 UTC+2 skrev Ricketty C:
On Tuesday, July 21, 2020 at 3:47:40 AM UTC-4, Clifford Heath wrote:
For electric cars, the measure is newtons, the force required to
maintain velocity against drag.
Newton is not useful since it will vary hugely over speed and only be useful to compare cars directly while saying nothing about what you really care about, cost.

But that\'s not what people actually use. You put kWH into your battery,
you get km out. The ratio of those is in newtons.

>>> What really matters is $/mile or €/mile, etc.

The future cost per kW is unknown when you choose a car.

People choose based on full-charge km (can it go where I need to go
without a recharge) and efficiency, in kWH/km (should be n).

Since the cost of electricity varies widely the energy per mile is useful as joules/mile or more commonly, even if not SI, kWh/mi. Of course these numbers will be related to driving patterns, but not the huge, direct impact that newtons suffer, just the same smaller effect we are used to with MPG.

What *are* you wittering about? The dimensions of joules/mile is newtons!

joule = newton metre
joule/metre = newton

Clifford Heath