TZ-OPT-MC built-in master controller, sliding cover hides the master controller after setup. Optional GPS interface available. Operate multiple displays. Synchronized time for up to 24 world time zones. 12/24 hour format, with or without seconds. 2.3" and 4" height super bright LED digits. Visible up to 110ft and 200ft away. Attractive black anodized aluminum enclosures. From one zone to ten zones in a single enclosure. Enclosures can be stacked as required. Applicable for boardrooms, trading rooms, hotels, airports and zulu clocks.