"John" wrote in message
om...
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.


That is called the heat anticipator, and yes..it does indeed effect the
stat.
You set the anticipation setting to that setting that the furnace states,
and leave it alone. It influences the spring stat and will prevent your
furnace from overshooting, or short cycling.