Why anyone would fool around with an old mechanical thermost which when
set for 62 gives a temp that varies from 66 to 70 or pay someone $30 to
come look at it is beyond me. For a little more you can buy a nice
accurate and programmable digital one that's very simple to install.

I don't understand why OP cares, anyway. You set the thermostat
(during the heating season) to the lowest value that you're
comfortable in. Who gives a **** what that temperature is labled, on
the dial?