How do you report hours that vary week to week? - any advice?

I picked up part-time shifts as an accountant and I am confused about how to report them. I would rather hear the honest version than the polite one. The form asks for gross earnings, which I do not see until later. Who can I ask without risking my claim?

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