"Sriram Narayan" wrote:
The only time I had seen a significant change in altimeter setting was when
crossing over from the central valley in California (Bakersfield sector) to
the LA basin (Socal). I remember my altitude was off by 100-150ft which
really bothered me and I could do nothing about it since I switched to the
altimeter setting provided when given to me. One of them was certainly off
for sure.

Are you saying that the mode-c altitude your transponder was reporting
differed by 100-150 ft from your indicated altitude? If that's the case,
your indicated altitude is considered the correct one.