Which clocks are considered the most accurate?

How do they know they're accurate over thousands of years?? They haven't been around that long.

Gary, In the 1980/1990s they were selling an expensive light bulb , called the Enterpriser I think , guaranteed for 100 years . Who keeps their grandparents receipts to take it back if they don’t get full term?

I have one on my coffee table. It also tells the day of the week and the inside and outside temps. Not expensive either

Gary, the basis of the claim is in the physics of the meathod used to make the measurement. The intrinsic error of measurement within an Atomic clock is extremely small, meaning that the cumulative error is that low. But the other types of clock have much larger intrinsic errors that require them to be adjusted at much smaller intervals, between a few months to a few years.

All I know is I bought an alarm clock that supposedly set itself by an atomic clock and it was always 5 minutes slow. Very strange.

starjumper, cool huh! but it isn't an actual atomic clock, on the coffee table, right? Just is synced to one and always accurate, just like our smartphones everyone has...

Gary, that's what I was wondering, too!

Sorry, never heard about atomic clocks.

Cesium fontain

dollis1963, they're about the same size as a small computer server and can cost as little as £10,000