- The built-in altimeter uses a pressure sensor to measure the current air pressure.
- The measured air pressure is then used to provide an "estimate" of the current altitude.
- The electronic mechanism in the watch is pre-programmed with "ISA values" ("International Standard Atmosphere") used to convert pressure values into altitude values.
- The air pressure and temperature generally become lower as the altitude increases.
- These values define the connection between altitude, air pressure and temperature.