Jim Macklin wrote:
That is the highest pressure you can set on the Kollsman
window.



I can hardly see how it should affect VFR flights. Additionally if the
pressure is higher than 31 inch mercury and the altimeter is set to
3100, the true altitude would be higher than what's indicated by the
altimeter. For VFR flights this would almost never introduce any
problems. (Even for IFR terrain separation this allows a bigger margin
for terrain clearance).

The only problem I could think of is the mode C requirement for
altitude above 10,000 MSL, if someone flying without a mode C x-ponder,
set their altimeter to 3100, on day with pressure higher than 31"
mercury, and flying right near 10,000 feet indicated on their altimeter
:-)