Mode C Indication

Jeff wrote:

In everyone's observation, what is the typical difference between the
indicated altimeter reading with current pressure setting and the altitude
reported by mode c transponder. It seems mine always has a discrepancy of
100', sometimes 200' compared to what ATC shows.

As far as I understand, your mode C will be reporting pressure altitude to
ATC, and their computers will adjust that based on the altimeter setting in
use for the sector. So the difference between the mode C and indicated
altitude can be huge, but I don't think that's what you're asking.

What happens on the ground when you set your altimeter to the station
altimeter setting? How far off is it from the field elevation?


All the best,


David