A rain gauge is a tool that measures how much rain falls. The simplest kind is a clear tube with lines and numbers on the side, like a ruler. You place it outside in an open spot, away from trees and roofs, so that rain can fall straight into it.

After a storm, you read the number at the top of the water. If the water reaches the line marked 1, then one inch of rain fell. Remember to empty the gauge after you read it. Otherwise, rain from the next storm will be added to the old water, and your measurement will not be accurate. Many weather watchers check their gauge at the same time every day and write the number in a notebook. After a month, they can see which weeks were wet and which were dry.