Compare two values from different times

Hi folks! I am new to Flux, so I expect I’m missing something simple.

I have a measurement with a count, a monotonically increasing value, in a field. I currently update it every 10 minutes.
I would like to query for how much it’s increased every day–or perhaps over another flexible period.
For example, “On Wednesday we added x users. On Thursday, we only added y.”
Can someone put me on the right track? Thanks!