Clearing The Logbook History; Effect Of Air Temperature On Altitude Measurement - Suunto Observer Instruction Manual

3.5.1 Clearing the Logbook History

To clear the history of the logbook:
1. In any of the logbook history screens, press the [SELECT] button for 2 seconds. The top
field displays the text "CLR", the middle field the text "HIS", and the bottom field the text
"nO". All three messages will begin to flash.
2. Press either the [ON OFF] or the [QUICK] button to toggle between "YES" and "nO".
3. Press the [MODE] button to accept the preference "YES" and exit.
The logbook history is erased and a new starting date will be set to begin new cumulative
measurements.
NOTE: Setup mode will automatically exit if left idle for more than one minute.
We recommend that the logbook history be cleared prior to beginning logbook recording(s).

3.6 EFFECT OF AIR TEMPERATURE ON ALTITUDE MEASUREMENT

The atmospheric pressure means the weight of air mass above the observer: at a higher
altitude there is less air than at a lower altitude. The principle of an altimeter is to measure the
different air pressure between different altitudes.
The outside temperature affects the air weight. Consequently the air pressure difference
between two altitudes is also dependant on temperature.
The altitude calculation of the Observer is based on the air pressure at certain normal
temperatures. Each altitude has a definitive normal temperature. The normal temperatures
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 Observer 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
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