Daimyo clock is a recreation of a mechanical clock developed in the seventeen century based on western clocks but modified to show traditional Japanese time.
Traditional Japanese time divides the day and night into six equal periods from dawn to dusk and dusk to dawn respectively. Over the course of a year as the daylight and nighttime periods lengthen and shorten, the length of these six day or night periods change. Unlike Western clocks which are regulated by a single pendulum and run at a constant speed day or night, Japanese clocks incorporated two pendulums, and switched between them at dawn and dusk. Adjustment for the changing daylight and nighttime hours was accomplished by adjusting the effective length of the pendulums, normally done every two weeks, or twenty-six times a year. This kept the time shown on the clock reasonably close to the correct time, provided that the clock had been set correctly initially.
This modern implementation is much more accurate and precise than the original clocks. In this implementation, the biweekly adjustments of the mechanical clock are made continuously, thus the day or night period length are always correct. Noon on the clock will, if location services are enabled, occur when the sun is at the zenith, or solar noon. Day start and end correspond to the beginning or end of twilight, and are calculated accounting for the refraction of the Earths atmosphere.
There are three situations where the clock my not show the local time in the Japanese manner:
1. If location services are off, Daimyo Clock will show the time for Tokyo, Japan. 東京 will be displayed on the clock face in this case.
2. While the application is obtaining an updated location after launch or returning to foreground.
3. Near the North or South poles the sun may either be above the horizon or below it for the entire day (24 hour period). In this case, the Japanese definition of time no longer applies, so the clock face will be shown without a clock hand.