Suunto Observer Instruction Manual page 28

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 Observer
shows 80 m too little (20 ºC * 2000 m * 0.002/ºC = 80 m). Your actual altitude is thus 3080 m.
All Suunto products with altimeter are temperature calibrated. This means that at constant
pressure, the reading of the pressure sensor is always the same independent of the unit's
own temperature. However, the air temperature can still effect the altitude readings as
described above.
Set reference altitude (real altitude)
Displayed altitude
Real outside temperature
Normal (table) temperature
Temperature offset (= real - normal)
Sum of temperature offsets
Table 3 shows an example in which the temperature offsets are negative. This time imperial
units are used. The reference altitude is set at 3280 feet. At 9840 feet the altitude difference
is 6560 feet and Observer shows 100 feet too much (-14 ºF * 6560 ft * 0.0011/ºF = -100 ft).
Your actual altitude is thus 9740 ft.
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Table 2. Example using meters and Celsius
Lower point
1000 m
+17.5 ºC
+8.5 ºC
+9 ºC
+9 ºC + +11 ºC = 20 ºC
Higher point
3000 m
+6.5 ºC
-4.5 ºC
+11 ºC