Originally Posted by
Discorde
Adjusting GPS altitude to match indicated barometric altitude would be accomplished electronically within the apparatus without pilot input required.
And where would this gadget get its input data from? As I said, the gadget needs the local QNH and the actual local environmental lapse rate (+humidity) of the whole column of air below you, to do the calculation. Otherwise your electronic gadget is just going to be a GIGO system (Garbage In - Garbage Out).