Hi Carlo, let me explain.
In our pressure sensors, each device is calibrated at the factory and the trimming coefficients are stored in the register map. They are read in the bmp180_get_calib_param function, called automatically within bmp180_init.
For each data point, you must trigger both temperature and pressure measurements, then call the API in this order:
bmp180_get_uncomp_temperature
bmp180_get_uncomp_pressure
bmp180_get_temperature
bmp180_get_pressure
Point #3 is especially important, since the temperature is stored in an internal value that is used in the pressure calculation. This is also why you must read both temperature and pressure at the same time. (temperature can be sampled on its own, but pressure measurements require temperature compensation).
The mathematical formulas are on page 15 of the datasheet, but the actual meaning of it is proprietary.
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