The 255 Series Evaporation Stations are complete systems used to measure the amount of water lost each day to evaporation. There are two commonly used procedures for making these measurements. In both, a U.S. National Weather Service Class A Evaporation Pan, 10 inches deep and 47.5 inches in diameter, holds the water and is normally installed on a wooden platform set on the ground in a grassy location.
One alternative for measuring the daily evaporation loss is to use a graduated hook gauge set on a Stillwell to determine the water level in the pan. The hook gauge is adjusted until the point just breaks the water surface, and a reading is taken from the attached scale. The second alternative uses a Stillwell with a fixed point. The graduate has a surface area of 1/100 that of the pan, so that the amount of water added is the equivalent evaporation. |
