Here, a rain gauge is installed which can be used to measure the rainfall everyday. A collecting jar is present at the lower portion of the rain gauge. The water collected in it in the past 24hrs can be measured using the measuring jar.

What did you observe? 
Rainfall data for that locality in centimeters for the past 24hrs can be obtained.

The science behind it :
Rain gauge is a device used to measure the rainfall. The volume of rain water measured(in cubic centimeters) is divided by the value of cross-sectional area(in square centimeters) of the Rain gauge’s opening at the top. Thus we can obtain the rainfall data(in centimeters) which is essential for designing dams, irrigation structures and for agriculture.