"Jim Macklin" wrote in message
...
they give altitude, accurate to within a few feet. just set
the altimeter to read the same. then you know adjusted
pressure. considering the legal requirements, it is
perfectly adequate.

First of all, no they don't give altitude accurate to within a few feet.
Secondly, they give a completely different kind of altitude measurement than
the altimeter provides. Even if the GPS were accurate to within feet for
altitude, setting your altimeter to the GPS displayed altitude would not be
the same as having the current, local altimeter setting.

Pete