SUUNTO X6OG - Manual (Page 52)

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The outside temperature affects the air weight. Consequently the air pressure differ-
ence between two altitudes is also dependant on temperature.
The altitude calculation of the Suunto X6 is based on the air pressure at certain normal
temperatures. Each altitude has a definitive normal temperature. The normal tempera-
tures at each altitude are presented in Table 1.
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 the Suunto X6 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 differ-
ence 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 the Suunto X6 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 independ-
ent of the unit’s own temperature. However, the air temperature can still effect the
altitude readings as described above.