I bought a Casio mountaineering watch, but I can't judge the weather from the change of air pressure.

This mountaineering watch is LCD, so it is easy to judge. Press "BARO" key to see the air pressure value, air pressure trend chart and temperature on the screen. If the curve in the barometric trend chart goes up, it means the weather is getting better, and if the barometric curve goes down, it means the weather is getting worse. Moreover, your watch has a very good function, that is, the storm warning function, which will remind you if the air pressure rises or falls too much or the weather changes suddenly. In this way, you can play outdoors without being disappointed by the sudden weather conditions.