"Dave" wrote in message
. net...
(snip)
Either the altimeter or encoder is off. Your allowed 125 foot deviation
between the two to be legal.
(snip)

Hmmm . . . interesting. Sometimes I fly over a local airport where the
controlled airspace tops out at 2,800'. Over that is Class B airspace with a
floor of 3,000'. So, I fly at 2,900' and figure I'm okay.

If my encoder is 125' different than the altimeter reading, I could be
reporting to either the tower or to ATC that I was infringing on their
airspace. Come to think of it, last time I flew over that tower (at 2,900'),
I requested a transponder check and they reported that I was showing 2,800'.
They didn't seem to get upset.

IIRC, the encoder reports in 100' increments, so I guess mine could be
anywhere from 49' to 149' off the altimeter. (it is VFR certified BTW).

Rich S.