Build size and comparison to main:

This all looks good, but I think the calibrating variable should be refactored into a state enum instead as it's currently somewhat unintuitive and the 255 value doesn't help. Perhaps something like States {Idle, PrepareToCalibrate, Calibrating, CalibrationDisabled}? These probably aren't the best names, I haven't thought about them much. Hopefully you get the idea though

This also has the issue that the text stays on the screen behind the other menu items if you leave the shake calibration screen since lv_obj_clean() is not called.

Pull request #2268 enhances and replaces this one.