units of measurement on altimeters

Do all commercial aircraft that fly in and out of North America have
dual unit altimeters (hPa and inHg)?

(Pat Norton) wrote:

Do all commercial aircraft that fly in and out of North America have
dual unit altimeters (hPa and inHg)?

I don't know about that, but as regards to the metric system, I would
like to mention that using hPa is _not_ the recommended way. Although
the "h" prefix is formally part of the SI system, it's regarded as
unsuitable by many, including NIST.

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

On Sun, 7 Mar 2004 16:18:10 +0000 (UTC), "Jukka K. Korpela"
wrote:

(Pat Norton) wrote:

Do all commercial aircraft that fly in and out of North America have
dual unit altimeters (hPa and inHg)?

I don't know about that, but as regards to the metric system, I would
like to mention that using hPa is _not_ the recommended way. Although
the "h" prefix is formally part of the SI system, it's regarded as
unsuitable by many, including NIST.

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

Amen.
http://ourworld.compuserve.com/homep...d/hectopas.htm

This screwball unit is just a misguided effort to hang onto an
obsolete unit by cloaking it in a marginally SI name. It makes no
more sense than soils scientists measuring soil conductivity (or
whatever is the proper term for the quantity measured, I'm doing this
off the top of my head without checking the terminology used) in units
of "dS/m".

Can you figure out the ever-so-handy unit the soils scientists are so
desperately trying to salvage?

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

"Gene Nygaard" wrote in message
...
On Sun, 7 Mar 2004 16:18:10 +0000 (UTC), "Jukka K. Korpela"
wrote:

(Pat Norton) wrote:

Do all commercial aircraft that fly in and out of North America have
dual unit altimeters (hPa and inHg)?

I don't know about that, but as regards to the metric system, I would
like to mention that using hPa is _not_ the recommended way. Although
the "h" prefix is formally part of the SI system, it's regarded as
unsuitable by many, including NIST.

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

Amen.


What about the pieze = 1000 pascals?

On Sun, 7 Mar 2004 20:42:10 -0000, "S Green"
wrote:


"Gene Nygaard" wrote in message
.. .
On Sun, 7 Mar 2004 16:18:10 +0000 (UTC), "Jukka K. Korpela"
wrote:

(Pat Norton) wrote:

Do all commercial aircraft that fly in and out of North America have
dual unit altimeters (hPa and inHg)?

I don't know about that, but as regards to the metric system, I would
like to mention that using hPa is _not_ the recommended way. Although
the "h" prefix is formally part of the SI system, it's regarded as
unsuitable by many, including NIST.

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

Amen.


What about the pieze = 1000 pascals?

The International System of Units is a meter-kilogram-second system of
units.

That mts unit of pressure is no more SI than the cgs unit of pressure,
the barye equal to 0.1 Pa.

Note that bars are so obsolete that they never did fit into any of the
many different coherent systems of units--not only do they not fit in
SI or any other coherent meter-kilogram-second system, but they did
not fit in centimeter-gram-second systems and they did not fit in
meter-ton-second systems.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

"S Green" writes:
What about the pieze = 1000 pascals?

http://www.unc.edu/~rowlett/units/dictP.html

pieze (pz)

a metric unit of pressure, part of the "metre-tonne-second" system
sometimes used by European engineers. The pieze is a pressure of
one sthene per square meter, or 1000 newtons per square meter,
or one kilopascal. [...]
The name of the unit comes from the Greek piezein, to press.
The unit, spelled pièze in French, is pronounced "pee-ezz" in English.

Interesting. I had never heard of a metre-tonne-second system
before. Where was it invented and in which fields was it used?

Markus

"Markus Kuhn" wrote in message
...
"S Green" writes:
What about the pieze = 1000 pascals?

http://www.unc.edu/~rowlett/units/dictP.html

pieze (pz)

a metric unit of pressure, part of the "metre-tonne-second" system
sometimes used by European engineers. The pieze is a pressure of
one sthene per square meter, or 1000 newtons per square meter,
or one kilopascal. [...]
The name of the unit comes from the Greek piezein, to press.
The unit, spelled pièze in French, is pronounced "pee-ezz" in English.

Interesting. I had never heard of a metre-tonne-second system
before. Where was it invented and in which fields was it used?

Markus

Well as I said our aircraft has the manifold pressure in pieze

ie 27 inches = 90 pieze approx

"Jukka K. Korpela" wrote in message
. ..

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

How can you possibly suggest that it would be more "practical" to use kPa?
There is an installed base of tens of thousands of altimeters in aircraft
out there that are calibrated in mbar. Describing them as hPa makes it
clear what the unit is for someone familiar with the SI, without risking
accidents through unit confusion.

The preference to use powers of 1000 is just a preference because
practicality and pragmatism is sometimes more important than an arbitrary
recommendation. This is a perfect example of where pragmatism should (and
does) win.

Julian Scarfe

"Julian Scarfe" wrote:

How can you possibly suggest that it would be more "practical" to
use kPa?

Because one digit less is needed, and conversions are easier when
powers of 1,000 are used as normally.

There is an installed base of tens of thousands of
altimeters in aircraft out there that are calibrated in mbar.

This is not about calibration, this is about expressing physical
quantities. Besides, if the installed base of equipment were decisive,
each of us would still use one's country's inch, pound, or whatever
local measures were in use long ago.

Describing them as hPa makes it clear what the unit is for someone
familiar with the SI, without risking accidents through unit
confusion.

Would it be clearer to use a non-recommended prefix than a recommended
prefix? Besides, your argument indicates a fundamental confusion. There
is only one SI unit of pressure, the pascal (Pa). That's part of the
beauty and practicality of the system. All the rest that is used to
express pressures relates just the way of expressing the numerical
value. For convenience, we can use multiplier prefixes of _the_ unit if
we like, or a multiplier of the number, consisting of a power of ten.

The preference to use powers of 1000 is just a preference because
practicality and pragmatism is sometimes more important than an
arbitrary recommendation. This is a perfect example of where
pragmatism should (and does) win.

The reason for preferring powers of 1,000, explicitly expressed in
several recommendations and standards, is its practicality, based on
the use of the system as a whole. If you take arbitrary special
aspects, you can always find arguments in favor of using non-SI units
or non-recommended SI expressions - but then you lose all the benefits
of a unified system. Using hPA is a half-hearted "solution" that
combines the trouble of transition (after all, it needs to be
introduced to people who didn't know it, and they need to be reminded,
and some people will inevitably misunderstand or forget) with the
effect of gaining almost nothing. (We _can_ convert millibars to
pascals too.)

--
Yucca, http://www.cs.tut.fi/~jkorpela/

"Jukka K. Korpela" wrote in message
. ..

Describing them as hPa makes it clear what the unit is for someone
familiar with the SI, without risking accidents through unit
confusion.

Would it be clearer to use a non-recommended prefix than a recommended
prefix? Besides, your argument indicates a fundamental confusion. There
is only one SI unit of pressure, the pascal (Pa). That's part of the
beauty and practicality of the system. All the rest that is used to
express pressures relates just the way of expressing the numerical
value. For convenience, we can use multiplier prefixes of _the_ unit if
we like, or a multiplier of the number, consisting of a power of ten.

I'm not sure where you believe the "confusion" lies. Describing the unit as
hPa rather than mbar makes it clear that the unit is Pa and the prefix,
which is a standard SI prefix, gives the multiplier.

The preference to use powers of 1000 is just a preference because
practicality and pragmatism is sometimes more important than an
arbitrary recommendation. This is a perfect example of where
pragmatism should (and does) win.

The reason for preferring powers of 1,000, explicitly expressed in
several recommendations and standards, is its practicality, based on
the use of the system as a whole. If you take arbitrary special
aspects, you can always find arguments in favor of using non-SI units
or non-recommended SI expressions - but then you lose all the benefits
of a unified system.

Do you really believe that you lose *all* the benefits of a unified system
by using a prefix described (without deprecation, BTW) in the SI Brochure?

Using hPA is a half-hearted "solution" that
combines the trouble of transition

One man's half-hearted solution is another's essential compromise. :-)

Julian Scarfe