I've read through the archives, but I still need some clarification. I know that the altitude is dependent on the pressure, and that any pressure changes directly affect the altimeter. Do any changes in altitude directly affect pressure readings? I would assume it would, but I'm no expert. I do know that my Riseman is very accurate with pressure readings at a constant altitude, but when traveling across a distance by car the pressure readings vary depending on considerable altitude changes. I don't calibrate the altitude very often. Any help is appreciated.