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

I work some days through a staffing agency while still certifying. It has been a long 18 weeks. The form asks for gross earnings, which I do not see until later.

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

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