One of our club members made this gauge to measure the thickness in the bottom of a bowl. The ruled section zeroes to the front surface of the chuck. The curved device is equal to the spindle height of the lathe. When slid to the center of the bowl the lower straight edge covers the colored rule. The visible measurement equals the wood left in the bottom of the bowl. Sliding Pieces are made to fit the ways of the desired lathe. This device takes all the guess work out and is dirty simple to use.