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.
However, OSB is generally considered less resistant to water (it swells in thickness when exposed to moisture) and some people prefer plywood for roofs and subfloors. The Miami-Dade County Board of County Commissioners banned OSB for use as roof sheathing after Hurricane Andrew destroyed thousands of homes in 1992.s OSB is cheaper than plywood and has the strength and durability of plywood it is becoming more widely used than plywood. OSB was introduced in the 1970s and steadily gained market share from plywood, surpassing plywood in production in 2000. Today OSB has 70-75% market share and plywood has about 25% share.