I have simply taken a Vierkantholz the lying around with me and had then set centrally and with a Feistel (heavy hammer) it added a few strokes. After every 2-3 beats I've tested with an angle if the ground is flat. After about 8 strokes the ground was then thoroughly plan.
Of course, a little annoying because with reasonable final controls so that could be avoided. But no doomsday. Worse, it would have been if the pan would have arched due to heat development.
Should change what, I'll add later in the review.