A float type rain gauge works the same way as the fuel gauge in a car. A floating unit made of something like styrofoam or a hallow rubber ball (anything that floats on water) is connected to one end of a lever arm. The other end of the lever arm is connected to an electric resistor that is connected to an electrical system. As the float rises due to water filling up the rain gauge, the lever arm adjusts the resistor to change the amount of current that flows through the system. The electrical current also flows through some type of readout device, usually a needle pointing to a measuring scale. As the current is altered by the level of the float changing, the needle on the readout device changes accordingly to show the amount of rain in the gauge.