Wage reporting when hours change weekly - what worked for you?

My hours change every week at my new part-time job and I am afraid of reporting wrongly. The form asks for gross earnings, which I do not see until later.

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.