This section is from the book "Hill's Manual Of Social And Business Forms: A Guide To Correct Writing", by Thos. E. Hill. Also available from Amazon: Hill's Manual Of Social And Business Forms: The How-To-Do-Everything Book Of Victorian America.
To find the number of feet in a board 1 inch thick from 3 to 30 inches wide, and from 4 to 24 feet long, see the following table. Explanation.- The figures at the top of the columns indicate the number of feet in length; those at the extreme left the width of the board in inches. To ascertain the number of feet multiply the number of feet in length by the number of inches in width and divide the product by 12, the result will be the number in feet and inches. Thus, multiply 9 inches wide by 13 feet long, and the result will be 117. Divide this by 12 and we have the product 9 feet and 9 inches. See the table.