Many years ago, I was at a physics seminar and Nasa engineers were showing us the tile technology they were going to use on the shuttles. One of the problems they faced was getting just the right amount of adhesive under the tile. Too much and it wouldn’t cool the inside. Too little and it wouldn’t hold. Some one discovered that if they took a bathroom plunger, and compared the sound that it made being pulled from the tile that they could tell when it was correct.