"A Lieberman" wrote in message
...
On Fri, 01 Apr 2005 14:19:56 -0600, O. Sami Saydjari wrote:

Sami

Well, I thought it was 0.5 inches, but I am not absolutley certain...it
was a while back. But, I do not think this changes my point
substantially. Even a 0.25 inch change is substantial, and if there is
not a standard of when one changes settings, it seems like a risk,
albeit small.

The .25 inch change was over 684 NM. Unless you are crossing a cold front
or a rather intense low pressure, you are not too likely to experience a
significant pressure change to the point that you describe.

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. Also, the radio comm was weak in the transition area. The Socal
controller was not too happy.