Editing Clock (section)

===Devices that measure duration, elapsed time and intervals===

[[File:Wooden hourglass 3.jpg|thumb|upright|The flow of sand in an [[hourglass]] can be used to keep track of elapsed time.]]

Many devices can be used to mark the passage of time without respect to reference time (time of day, hours, minutes, etc.) and can be useful for measuring duration or intervals. Examples of such duration timers are [[candle clock]]s, [[incense clock]]s, and the [[hourglass]]. Both the candle clock and the incense clock work on the same principle, wherein the consumption of resources is more or less constant, allowing reasonably precise and repeatable estimates of time passages. In the hourglass, fine [[sand]] pouring through a tiny hole at a constant rate indicates an arbitrary, predetermined passage of time. The resource is not consumed, but re-used.