Why So Many Units?...

[Ricketty C]

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

 

[Mikko OH2HVJ]

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..

--
mikko

 

[Mikko OH2HVJ]

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..

--
mikko

 

[Martin Brown]

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.

--
Regards,
Martin Brown

 

[Martin Brown]

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.

--
Regards,
Martin Brown

 

[Martin Brown]

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.

--
Regards,
Martin Brown

 

[Mikko OH2HVJ]

Martin Brown <\'\'\'newspam\'\'\'@nezumi.demon.co.uk> writes:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
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.

I\'ve seen cmH2O used with ventilators and anaesthesiology in
Finland. I\'ve understood that there\'s some difference even between the
Nordics in this field. mmHg for blood pressure - forgot that.

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.

Discussing about gas mixing and physiology with anaesthesiologists and
other docs was an interesting one for an engineers. Fortunately I\'ve
learned to disregard things like non-SI units - learned a lot both ways!

--
mikko

 

[Mikko OH2HVJ]

Martin Brown <\'\'\'newspam\'\'\'@nezumi.demon.co.uk> writes:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
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.

I\'ve seen cmH2O used with ventilators and anaesthesiology in
Finland. I\'ve understood that there\'s some difference even between the
Nordics in this field. mmHg for blood pressure - forgot that.

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.

Discussing about gas mixing and physiology with anaesthesiologists and
other docs was an interesting one for an engineers. Fortunately I\'ve
learned to disregard things like non-SI units - learned a lot both ways!

--
mikko

 

[Piotr Wyderski]

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\".

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

Best regards, Piotr

 

[Piotr Wyderski]

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\".

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

Best regards, Piotr

 

[server]

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.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

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.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Mikko OH2HVJ]

Martin Brown <\'\'\'newspam\'\'\'@nezumi.demon.co.uk> writes:

On 20/07/2020 09:14, Mikko OH2HVJ wrote:
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.

I\'ve seen cmH2O used with ventilators and anaesthesiology in
Finland. I\'ve understood that there\'s some difference even between the
Nordics in this field. mmHg for blood pressure - forgot that.

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.

Discussing about gas mixing and physiology with anaesthesiologists and
other docs was an interesting one for an engineers. Fortunately I\'ve
learned to disregard things like non-SI units - learned a lot both ways!

--
mikko

 

[Tauno Voipio]

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.

--

-TV

 

[Tauno Voipio]

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.

--

-TV

 

[Tauno Voipio]

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.

--

-TV

 

[server]

On Mon, 20 Jul 2020 18:35:34 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> 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.

Weather maps and reports use inches of mercury here. A bad hurricane
can get down to something like 28.

Shop and tire pressures are in PSI.

How do Europeans measure tire pressure?

We use all SI for engineering, except PCB layout is in decimal inches.
At least we don\'t work in fractions. Much.

We cook in cups, pounds, ounces, degrees F, pinches, tablespoons, all
sorts of fun stuff.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Mon, 20 Jul 2020 18:35:34 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> 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.

Weather maps and reports use inches of mercury here. A bad hurricane
can get down to something like 28.

Shop and tire pressures are in PSI.

How do Europeans measure tire pressure?

We use all SI for engineering, except PCB layout is in decimal inches.
At least we don\'t work in fractions. Much.

We cook in cups, pounds, ounces, degrees F, pinches, tablespoons, all
sorts of fun stuff.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Mon, 20 Jul 2020 18:35:34 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> 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.

Weather maps and reports use inches of mercury here. A bad hurricane
can get down to something like 28.

Shop and tire pressures are in PSI.

How do Europeans measure tire pressure?

We use all SI for engineering, except PCB layout is in decimal inches.
At least we don\'t work in fractions. Much.

We cook in cups, pounds, ounces, degrees F, pinches, tablespoons, all
sorts of fun stuff.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Clive Arthur]

On 20/07/2020 16:52, jlarkin@highlandsniptechnology.com wrote:

<snip>

Weather maps and reports use inches of mercury here. A bad hurricane
can get down to something like 28.

Millibars here.

Shop and tire pressures are in PSI.

How do Europeans measure tire pressure?

Bars - a bar is defined as 100kPa which is pretty much sea-level
atmospheric pressure.

In the UK psi are often used too, though for tyres, not tires.

We use all SI for engineering, except PCB layout is in decimal inches.
At least we don\'t work in fractions. Much.

It\'s a shame an inch isn\'t 25.6mm instead of 25.4mm.

We cook in cups, pounds, ounces, degrees F, pinches, tablespoons, all
sorts of fun stuff.

Older people would use most of those, except that \'cups\' aren\'t used
here. If they\'re not metric, shoe size increments still use
barleycorns, but few people know that.

The difference between Celsius and Fahrenheit was recently explained on
a radio programme. \"Celsius is a temperature scale where zero degrees is
the freezing point of water and one hundred degrees is the boiling point
of water, whereas Fahrenheit is wrong.\"

Euro paper sizes are neat. A0 is one square metre, so A4 is 1/16 m^2
which means a single sheet of \'normal\' 80gsm printer paper is 5g which
happens to be the same weight as a 20p piece. (And three pre-decimal
pennies weighed one ounce so £1 of copper coinage would weigh 5lb.)

Trivia.

--
Cheers
Clive