This is a mercury switch type thermostat. It controls both my A/C and gas heat in my house. There is a adjustment arm on the inside that can be moved from .18 to 1.0 and an arrow pointing to the 1.0 that says "longer." What does this adjust? I have set it to 1.0 in hopes that a/c will not cycle on/off asoften as it does. Right now it comes on and runs for 8-9 minutes shuts down and then starts up in another 8-9 minutes.