Candle clocks marked time by burning evenly, with markings showing how much had melted.

The longer version

A candle made to burn at a predictable rate becomes a timer: marked bands down the wax show how much has been consumed, and reading the lowest visible mark gives the elapsed interval. Thickness, wax quality and wick all affect the burn. Each band corresponded to a fixed portion of the night.

Draughts ruin accuracy, so these were used indoors and often enclosed. They were popular in monasteries and households because a single object gave both light and a rough schedule through the night. Households kept marked candles for night watches long after mechanical clocks existed, though burning rate varied enough that no one relied on them for precision.

Where this entry sits

These facts wander through clocks, calendars, time zones, and the long human effort to measure passing hours. You will find leap years, odd month lengths, ancient sundials, and the reasons modern timekeeping works the way it does. The full list sits on the Time and Calendars page, where every entry is listed in order.