Did you know what time it was when you got up this morning?
Did you get up at 8am and find it was really 9am, because you'd forgotten to put your clock forward an hour?
It's exactly 100 years since the practice, known as daylight saving, was adopted in the UK.
We were in the midst of the First World War, and the aim then was to save fuel, and give people more time to work in the fields.
It's a tradition that's stuck, with clocks put forward one hour on the last Sunday in March, to mark the start of British Summer Time (BST).
Today, the idea is to make the most of natural daylight, by arranging for the hours of the day when we do the most things to happen when it's light.
What it means in effect is that we lose an hour's sleep - but don't worry, we get it back on October 30, when the clocks go back an hour to mark the end of summertime.
Now, some people think that we should have British Summer Time all year round.
The lighter evenings are said to reduce road accidents and crime.
And it is argued that BST is good for your physical and psychological health, particularly in terms of relieving the symptoms of Seasonal Affective Disorder (SAD).