A sparse ruler is called optimal if it is both minimal and maximal. Since the number of distinct pairs of marks is m ( m â 1 ) / 2 {\displaystyle m(m-1)/2} , this is an upper bound on the length L {\displaystyle L} of any maximal sparse ruler with m {\displaystyle m} marks.
1 One 23/32-inch 4x8-foot plywood piece weighs approximately 67 pounds, while a piece of OSB of the same dimensions weighs approximately 78 pounds.
Plywood also has a slight advantage in stiffness, which means that subflooring panels need not be quite as thick. For instance, with 24-inch truss/joist spacings, the National Wood Flooring Association recommends nominal 1 inch OSB underlayment compared to 7/8 inch CDX plywood.