Precipitation is formed when the hydrometeore, hanging as clouds or fog in the air, are not longer supported by the upward air current. Then It is falling down to the earth (falling precipitation like rain, snow and hail) or deposited on the earth surface (deposited precipitation like white frost or white dew).
The fallen precipitation on the earth surface is mainly registrated as the height of precipitation in millimeters [mm]. This unit gives the height of water level on the earth surface provided the water doesn’t evaporate, or flow or seep away. Every millimeter of the height of precipitation is equal to an amount of 1 litre water per m² of earth surface. If the precipitation falls in solid form (e.g. as snow) the height of precipitation is determined by the molten precipitation.
The measurement of precipitation is simply done by collecting the precipitation. The rain gauge should stand free. No obstacles like buildings, trees or walls should be too near. The horizontal distance to such obstacles should at least be equal to the height of the obstacle. The precipitation that falls through the horizontal collecting area one meter above ground is collected in a can. For the measurement the content of the can is filled into a graduated cylinder and then the reading is taken. The measurement can also be taken by counting the tips of a tipping bucket beneath the funnel of the collecting area.