| Sundial | An ancient form of timekeeping using the position of the Sun. The time is estimated by the shadow that the gnomon, or pointer, casts onto a surface marked with lines. |
| Clepsydra/Water Clock | Originating from ancient Egypt, this system measures time by regulated flow of liquid (usually water) from or into a vessel. |
| Hourglass | A device where two glass bulbs are connected by a narrow neck. Sand or other fine granules flow through, measuring a set amount of time. |
| Candle Clock | Utilized in ancient China, Japan, England, and Iraq, these clocks determine time based on how long a candle takes to burn. |
| Mechanical Clock | From the 14th century onward, most clocks were made with a mechanical mechanism powered by a weight or a spring. The mechanism counts the swings of a pendulum or an oscillator, thus, keeping time. |
| Quartz Clock & Watch | Invented in the 1920s, these timekeepers use quartz crystals that vibrate in response to an electric charge, keeping very accurate time. |
| Atomic Clock | This clock uses the vibrations of atoms (usually cesium or rubidium) to keep time. It’s the most accurate timekeeping method that we have today. |
| Digital Clock | A type of clock that represents and displays time digitally, i.e., in numerals or other symbols, as opposed to an analog clock where time is indicated by the positions of rotating hands. |
| Binary Clock | A clock that displays traditional sexagesimal time in a binary format. |
| Marine Chronometer | A timepiece that is precise and accurate enough to be used as a portable time standard, allowing time to be determined accurately despite motion from sea travel. |
