CASIO PRG-550 THE WORKING PRINCIPAL OF SENSORS & CALIBRATION

Hello Everybody,

I just bought a CASIO PRG-550 (with sensor 5213) and I have some questions which I couldn't find answers, yet.
Whenever I calibrate the watchs barometer&altimeter at sea level to 1013mBa and 0 m accordingly, it goes wrong within 1-2 days later.
I assume that Altitude is to calculated according to the Barometer sensor values, right? So, the local changes at air pressure effect the altitude read outs. Do you agree?
If yes, everytime before trekking or climbing, I need to re-calibrate the watch at a "known" place "just" before the action. Is there any other way?

So, if altitude is determined by pressure, is there no any sensor for altitude? If yes, I really wonder the working principal?
The watch is mentioned as a 3-sensor watch. These 3 mean TEMP-COMP-PRES (with ALTI) or TEMP-PRES-ALTI?

Besides, sometimes ALTI shows -40/-50 meters but BARO showing 1010's (should be at positive meters).
So this make me think that BARO and ALTI are not completely connected to each other at this watch?

I would like to receive some help from you.

Thanks in advance.