A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel where the amount is then measured.
As civilisations developed, the designers of these clocks became aware of the factors which determined their accuracy, including the rate of evaporation of water from the vessel, the change of flow rate through the aperture with temperature due to expansion and the change in viscosity of the water, and the need to keep the water clean and free from impurities.
candle clock consisted of six candles made from 72 pennyweights of wax, each being 12 inches high, of uniform thickness, and divided into 12 sections each of one inch. Each candle burned away completely in four hours, making each marking 20 minutes
when the clock is blown out how could we know what is the timehour glass
An hourglass (or sandglass, sand timer, sand watch, or sand clock) is a mechanical device used to measure the passage of time. It comprises two glass bulbs connected vertically by narrow neck that allows a regulated trickle of material (historically sand) from the upper bulb to the lower one.
Factors affecting the time interval measured include the sand quantity, the sand coarseness, the bulb size, and the neck width.