Hickory, Dickory, Doc
I saw part of a TV show yesterday, ostensibly put on by Stephen Hawking, in which some people took a cesium (caesium) atomic clock to the top of a mountain while another person kept a similar clock basically at the foot of the mountain.
They kept the two clocks in those positions for 24 hours. The premise is that time runs more slowly the closer you are to the center of a source of gravity, like the earth.
So the one at the top of the mountain should run a wee bit faster than the one at the base.
Sure enough, it did, even if only by a few tiny fractions of a second.
It's this kind of super-accurate clock that you will work with today. You don't have to actually have one in your possession. I think you can find what time the official atomic clock reads online. Discounting time lag caused by the Internet itself, you should then be able to synchronize a clock you own with that official timepiece - or get it close enough.
Assuming you own a battery-operated clock, you'll probably want to do this again next year.
Does anyone still own a watch that you have to wind up every so often?
For the very young...Watches used to be spring-loaded and needed winding by a stem that protruded from them whenever the spring fully uncoiled itself.
No, really.