Why are there abrupt changes in elevation sometimes?
The sharp change in elevation may be due to a few things. One is changing ambient air pressure. This behavior signals the need to recalibrate the altimeter with either a known elevation or the barometric pressure. This also may be due to the unit performing an auto-recalibration that uses GPS elevation to set the altimeter. If the ambient air pressure has been rising over time and the altimeter elevation has climbed, an auto-recalibration based on GPS altitude may result in a sharp decrease in this altimeter elevation value. Otherwise, a sharp change in elevation means you have lost the satellite signal.
