system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do gas meters measure how much gas you use if gas can be compressed? (unlike water)
gpt
Because the gas is supplied at a set pressure.

There's a flow meter that reads the amount of gas that's gone through it.

So given a set specific pressure and a reading of how much has gone through it's very easy to know just how much gas has been used.