John wrote:
What does the copper pointer and the scaled piece over which it
travels control? The scale has the word "longer" stamped into it, but
it's not clear to me exactly what effect it has on the operation of
the thermostat.

I am not sure about that particular thermostat, but that sounds like the
anticipator control. Longer will mean the heat will stay on longer each
time it comes on. That usually translates to slightly wider temp swings and
slightly higher efficiency. The thermostat is guessing how long to leave
the heat on, knowing that if it waits until the temperature at the
thermostat gets up to the set temperature, and turns it off when that is
sensed the temperature is going to end up hotter than intended.

Usually you can just leave it were it came and not worry about it. That
is likely the best setting.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math