An instrument with lines, divisions, and numerals marked upon it, of the greatest utility in mensuration. There are, of course, numerous kinds adapted to their peculiar objects. The most extensively useful is unquestionably the carpenter's rule, for taking lineal measurements, which is therefore divided into feet, inches, and various parts, scales of proportion, etc. There are various sliding rules, for performing computations; others furnished with tables adapted to the use of all kinds of trades and manufactures, as well as professional persons. For rules especially designed for drawing parallel lines, see Parallel Rule.