43
1800
5906
3.3
37.9
2000
6562
2.0
35.6
2400
7874
-0.6
30.9
2800
9187
-3.2
26.2
3000
9843
-4.5
23.9
3400
11155
-7.1
19.2
3800
12468
-9.7
14.5
4000
13124
-11.0
12.2
4500
14765
-14.3
6.4
5000
16405
-17.5
0.5
5500
18046
-20.8
-5.4
6000
19686
-24.0
-11.2
Table 1. Normal temperatures corresponding to different altitudes
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 0.11% / 1 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 2 shows an example in which the temperature offsets are positive. In this example, the reference altitude
is set at 1000 m. At 3000 m the altitude difference is 2000 m and Wristop Computer shows 80 m too little (20
ºC * 2000 m * 0.002/ºC = 80 m). Your actual altitude is thus 3080 m.
