your altitude encoder may be off and need adjusting.

last year ATC was seeing me 200 ft lower then I was, I took it to the avionics
shop and he adjusted the altitude encoder, now ATC see's the same thing my
altimeter is saying.


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.

Just wondering if it needs further investigation. Pitot static, altimeter
and transponder inspections are all current.

Thanks!
Jeff