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 recovering a personal identification number. A method, includes: comprising recovering from a lost personal identification number situation and restoring programmability to a device, including: generating a SEED PIN using the device calculating a KEY PIN using an algorithm within a code of the device and storing the KEY PIN in the device, without displaying the KEY PIN, wherein the KEY PIN is a function at-least-in-part of both the SEED PIN and an identifier associated with the device; sending the SEED PIN and the identifier associated with the device to an authenticating source; recalculating the KEY PIN at the authenticating source using the algorithm within the code and the SEED PIN and the other identifying information; receiving the KEY PIN from the authenticating source; and entering the KEY PIN into the device to temporarily assign hierarchical access to a user.

Abstract: Systems and methods are described for recovering a personal identification number. A method, includes: comprising recovering from a lost personal identification number situation and restoring programmability to a device, including: generating a SEED PIN using the device calculating a KEY PIN using an algorithm within a code of the device and storing the KEY PIN in the device, without displaying the KEY PIN, wherein the KEY PIN is a function at-least-in-part of both the SEED PIN and an identifier associated with the device; sending the SEED PIN and the identifier associated with the device to an authenticating source; recalculating the KEY PIN at the authenticating source using the algorithm within the code and the SEED PIN and the other identifying information; receiving the KEY PIN from the authenticating source; and entering the KEY PIN into the device to temporarily assign hierarchical access to a user.

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.

Abstract: Systems and methods are described for a usage monitoring HVAC control method. A method, includes: receiving a request for an additional period of heating ventilation and air conditioning system services from a requesting system user, the requesting system user composing a plurality of system users; maintaining a data structure in an on board memory of a programmable thermostat, the data structure including a list of time entries, each time entry associated with one of the plurality of system users; and updating the data structure by adding a duration in units of time to the time associated with the requesting system user.