Abstract: Systems and methods are described for synchronizing an HVAC control system. A method, includes: a synchronization sequence including: reading a base time from an internal clock at a first time and saving the base time; measuring an elapsed time interval, from the first time to a second time, by counting an external clock using a frequency counter; and then resetting the internal clock to the base time plus the elapsed time.

Abstract: Systems and methods are described for an adaptive hierarchy usage monitoring HVAC control system. A method, includes: regulating user access to at least one menu of an interactive user interface of a programmable digital thermostat, including: reversibly defining at least one minimum user level required to access the at least one menu.