Wood Workers Rule

The only tape approved by the National Hardwood Lumber Association, the
Woodworker's Rule helps you determine surface measure (S.M). It reads as
a standard tape on the front, but the patented design on the back also
allows you to determine the "board feet" of hardwood. By using the
inches on the front and the four-line rule on the back, you can measure
any random width board or boards and accurately read the surface
measure. 16 ft. long with 3/4 in. steel blade.