How to repeat a formula automatically every nth rows?

Hi there,

I need to have a formula to repeat every 24 rows. This formula calculates the rate of change for every 24 hrs of inches of water in a tank in percentage.
I need to have this formula display every 24th row (for each new day)
There is no way I am going to do it manually for thousands of rows...

I don't know how to do this and any help would be greatly appreciated.


Thanks!