50
now the altitude measurement error caused by an abnormal temperature gradient can be approximated as follows.
If the sum of
the temperature offsets from the normal temperatures determined at two different altitudes is 1 ºC, the altitude difference
calculated by Wristop Computer is 0.2% off the real altitude difference
(When using imperial units the offset factor is 0.% /
ºf). this is because the real temperatures are not always the same as the normal temperatures. a higher than normal temperature
causes the calculated altitude difference to be smaller than the real altitude difference (your mountain ascent was actually higher).
consequently, a lower than normal temperature causes the calculated altitude difference to be larger than the real altitude difference
(you did not ascend quite as high as displayed).
table shows an example in which the temperature offsets are positive. In this example, the reference altitude is set at 000 m. at
3000 m the altitude difference is 000 m and Wristop computer shows 80 m too little (0 ºc * 000 m * 0.00/ºc = 80 m). your actual
altitude is thus 3080 m.
lower point
Higher point
set reference altitude (real altitude)
000 m
Displayed altitude
3000 m
real outside temperature
+7.5 ºc
+6.5 ºc
normal (table) temperature
+8.5 ºc
-4.5 ºc
temperature offset (= real - normal)
+9 ºc
+ ºc
sum of temperature offsets
+9 ºc + + ºc = 0 ºc
table 2. example using meters and celsius
