mpl3115a2 i2c altimeter example is returning -100m for me

[peterharperuk]

The temperature looks ok but the altitude looks wrong. Needs some study.

[lurch]

https://learn.adafruit.com/using-mpl3115a2-with-circuitpython/circuitpython says "To make the altitude calculation more accurate you'll want to set the pressure at sea level for your current location and weather conditions. Barometric pressure sensors can only calculate altitude based on the pressure of air they detect and that pressure changes daily and with weather conditions."
The example Adafruit Python code has a sealevel_pressure calibration, which appears to be missing from https://github.com/raspberrypi/pico-examples/blob/develop/i2c/mpl3115a2_i2c/mpl3115a2_i2c.c