We did a transponder/altimeter certification on a friend's glider in
my garage the night before last.
The 57mm Winter altimeter has only one external adjustment screw,
not the two of the 80mm units. This was an older altimeter, and needed
some help. It was initially 700 feet off at 4000' (home).
Help provided, both altimeter and encoder/transponder were taken
down to sea level, up to 20,000 feet, and certified. Cost was $160.00
with the tech coming to my house.
Will be doing the same with my glider (and a new 57mm altimeter) in
a week or two.
Incidentally, the adjustment screw is on the corner of the 57mm
altimeter's casing, and has wax in the access hole making it difficult
to identify. You must remove the altimeter from the panel to adjust.
Jim