"Matt Whiting" wrote in message
...
Mike Rapoport wrote:

"Matt Whiting" wrote in message
...

Mike Rapoport wrote:


"Andrew Sarangan" wrote in message
le.com...

Please explain how 2C/1000 is used in altimeter calibration. I did not
know altimeters had any temperature corrections.


Altimeters are preasure guages with a scale in feet. They assume a
pressure lapse rate with altitude and the pressure lapse rate that they
use is ISA whch assumes 15C at SL and 2C/1000'.

Last I knew C was a unit of temperature, not pressure.

Matt



Last I heard temperature had an effect on the density of any gas with the
consequent lowering (in feet) of any preasure level with decreasing
temperature. Remember "high to low, lookout below". Canada even has
altitude correction tables for use when temps are very low.

It does, I'm not disputing that. However, a gas can have the same
pressure at multiple temperatures, so knowing the temperature alone isn't
sufficient to make a pressure calibration.


Matt

The altimeter measures only pressure. Since pressure at any given altitude
varies with temperature so there had to be a convention on what the standard
temperature lapse rate would be and that was ISA which assumes 2C/1000'. My
only point is that knowing that the actual atmospheric lapse rate is 2C/1000
tells nothing about stability since the air can be either stable or unstable
at that lapse rate.

Mike
MU-2