- See: Hourglass figure
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| Hourglass (sand timer) |
An hourglass (or sandglass, sand timer, sand clock or an egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated trickle of material (sand) from the upper bulb to the lower one. Hourglasses may be reused indefinitely by inverting the bulbs once the upper bulb is empty.
Factors affecting the time measured by an hourglass are
- sand quantity
- sand coarseness
- bulb size
- neck width.