For eight months out of the year, the U.S. and dozens of other countries follow daylight saving time, and for the remaining four months, they revert back to standard time in order to take full advantage of the sunlight.

On the second Sunday of March at 2 a.m., clocks move forward one hour. Then, on the first Sunday of November at 2 a.m., the clocks turn back an hour.

There’s an age-old myth that daylight saving time was adopted to give farmers extra time in the sun to work out in the field. But that’s not really why dozens of countries follow it.

The practice was first used in Germany in 1918 during World War I as a way for troops to conserve fuel and electricity. Many countries followed suit, including the U.S., but later went back to using standard time after the war ended.

Then, President Franklin D. Roosevelt re-established daylight saving time nationwide on Feb. 9, 1942, during World War II. It lasted until the end of September 1945.

The U.S. didn’t standardize daylight saving time until 1966, when it passed the Uniform Time Act.

In the U.S., states are not required by law to follow daylight saving time. Hawaii and most of Arizona do not observe it, while other states – like Florida and California – are working to observe the system year-round.