pressure gauge Answered

Hello
I have a heat press that has no pressure gauge. I am trying to figure a way to add a manual one.
So when I close the upper platen to the bottom I can tell how much pressure is being exterted on to a substrate that I am pressing. If a way coudl be found to do it while being able to withstand 400+ degrees F that be great but if not doing it cold shouldn't matter.

Thickness would have to be less than a inch.

I was thinking a air bulb like on a blood pressure cuff and some type of gauge but not sure about that.

Anyone got any good ideas.
THanks
Mark