Valcom''s state-of-the-art analog clocks feature automatic communication protocol selection. The microprocessor-based movements recognize both 58th and 59th minute sync-wire as well as our Valcom 2-wire digital communication protocols. 2-wire digital communication protocol provides immediate time correction following power failures and time changes.For classroom applications, a single cable pull may be used to connect a clock, a speaker and a call switch thus saving thousands of dollars in dedicated clock cabling.Valcom clocks are compact, energy efficient and reliable. Valcom clocks save up to 85% of the energy used by other clock models on the market. The clocks are available in 12" and 16" round cases with durable, long-lasting polystyrene dials.