"Andy" wrote in message
ups.com...
My observation is based on analysis of many of my own flight logs. I
am so convinced this 100 foot difference is valid that, if there is no
local altimeter setting available, ....... snip
Andy

I also beleive the 100 foot (plus or minus) from take-off to landing is
valid.
It is called diurnial effect. The suns heating of the ground during the day
causes the pressure in the lower atmosphere to decrease slighly causing the
altimeter to read about 100 feet higher than actual. This is on most days,
we all know that weather facts are sometimes variable. Of course if you
land next to some mountains where there is down flow during the late
afternoon your milage (pressure) may vary.

Duane