Over the years i have always felt unsure about measuring V and concaves with the square. Recently I rode a long board i liked and wanted to be as accurate as possible about the bottom measurements. Now in my shaping bag of tricks I added 2 quarters,2 dimes and 2 nickels. By placing any combination of coins under the level either in the middle or by placing on the rails for V. One of the best things about this is that it is so consistent and available. I have now started testing myself when I look at a board to see if I can guess the cents value. Another trick I added is to push the rail of the coin into the foam as a reference to sand lower according to the coin depth still needed. Having handled coins my whole life its amazing how u just know the thickness. I added to my mid,nose and tail measurements on order card a place for cent values. Let me know how this works for you.
Surf Country Doug
