[pct-l] Watch and Altimeter

[adrian.borner at ch.abb.com (adrian.borner@ch.abb.com)]

As has been mentioned, a barometer and an altimeter are basically the same.
It just depends which of the variables you keep or at least assume as
constant. When using it as a barometer one must not change the altitude,
i.e. one is stationary while when using it as altimeter one assumes the
barometric pressure at a given heights remains the same (weather does not
change). As a result altitude readings are affected by the weather. However
the sensitivity to change in altitude is much bigger than change in
pressure due to weather conditions (I do not know the formula off hand).
Obviously when you run into a storm front then you will be completely off
with your altitude reading.
Temperature is another variable which affects the readings. As a result the
meters have a temperature compensation which is more or less accurate.
As said earlier, frequent recalibration is required. GPS with additional
barometric altimeter generally do this automatically. The barometric
altimeter is more accurate short term, while the GPS ensures long term
accuracy.
Hope I did not confuse the issue
Adrian