How are hourglasses so accurate/How do they work?

Question

I know that it’s possible to buy hourglasses that run out after a set amount of time, like 30 mins/an hour/2 hours etc., and even water-drippers that measure every 30 minutes. How do they do that?

In: 2

Answer 1

They’re not actually that accurate, hour glasses vary quite a bit across different hour glasses of the same “time” and even within the same hour glass on different uses.

But if you’re using an hour glass you don’t need that good of accuracy. Does it really matter if your 1 hour hour glass runs for 60 minutes and 15 seconds vs 59 minutes and 48 seconds? Not really.