One way to measure crown from the top side is to use a long stick, two looong screws and a dial indicator with a long plunger. Make it it to look like this |___|___|. You calibrate by adjust one of the screws so you get a zero Ö reading on the dial using a really flat surface. If you use additional screws you can check at many location well into the treble. The other easy way is to use a thread on the board between the longest ribs. Simple but a way even I can understand. Newton
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