allanc wrote:
It's a mechanical type.
I will take the cover off tomorrow in the daylight and try to get the
model number.
The unit is probably decades old.
Do you think the manual would actually have troubleshooting tips such
as when the temperature is off by 8 degrees?

If no LCD readout and buttons, it's mechanical. When you remove the
cover, check how the base is screwed to the wall. Likely a screw
at the top and a screw at the bottom and the screw at the bottom
may go thru an 'oblong' hole rather than round. If so, loosen the
top and bottom screws slightly and rotate the base slightly in one
direction. If that improves the accuracy, good. If it makes it worse,
rotate the base in the opposite direction. Does that improve
accuracy?

What this is all about is that mech Tstats are supposed to be
installed perfectly level and if not, accuracy can be off for some
mechanical Tstats.