How to flatten a warped record

I finally got around to replacing my long lost copy of The Stun Guns' And There Was Nothing We Could Do About it recently.  You can imagine my dismay when I got it home and found it unplayably warped. 

I stuck it between two pieces of glass - in this case a storm window and the front of a picture frame - and weighted it down with my change jar, leaving it in the sun for a couple of hours.

It worked!  At least enough that I can listen to the whole album now.  I got much better results with this than some of the other methods I've tried - the oven trick is too hard to predict, the wood stove was too hard to get to a steady low temperature, etc.  Science!