Traditional Japanese timekeeping consisted of six periods of daytime and six periods of nighttime. The pillar clock was designed in the early 19th century with an indicator on a dropping weight and movable labels (called toki) which could be adjusted for the differing length of periods of day and night throughout the year. The simple clockwork on top is regulated by a primative verge escapement and the strike is triggered by pins on the movable labels.

The six periods start from solar noon and midnight and run down from 9 (九) to 4 (四). The periods count down rather than up, following the original practice of measuring the length of candles as they burned down. The clock itself starts at sunrise, period 6 (六), presumably because it was more convenient to wind the clock at surise and adjust at sunset, rather than noon or midnight. The period numbers were chosen to end at 4, as the clock strikes each period and they wished to avoid conflicting with the significance of one to three gongs in Buddhism. All twelve periods also have a zodiac sign assigned to them.

With modern timekeeping now ubiquitous, these clocks no longer serve a practical purpose. However, they are highly sought after by collectors.