Distances of a few feet are usually measured with the ordinary foot rule graduated in inches, and in halves, quarters, eighths, and sixteenths of an inch. A carpenter's wooden rule is made of boxwood, because of all woods this is affected least by climatic conditions. Machinists' rules (Fig. 2) are usually made of hardened steel and are graduated to a fine degree.
Fig. 1. - Pint Graduate. Graduated on right by ounces, on left by fractions of a pint. The symbol in the center is the symbol for pint.
* The unit by which gas is measured is the cubic foot. The unit by which building materials are measured is usually the cubic yard.
For convenience in carrying in the pocket, foot rules (Fig. 3) are often made with hinged joints so that they fold into a short length (4 in. or 6 in.) and longer rules are made in multiples of a foot. Formerly the most common rule used by mechanics was the folding 2-ft. boxwood rule. Present-day mechanics also use this rule largely, but where greater lengths are to be measured the zigzag folding rule is more commonly employed. This latter rule folds into 6-in.
sections and may be obtained in any length up to 10 or 12 feet. The yardstick (3 ft. long), subdivided into feet, inches, and fractions of an inch, is also frequently used as a unit of measure, especially for the measurement of textiles.
In building construction and timber measurements a 10-ft. pole is often employed. It is usually divided into 1-ft. sections, with the first foot subdivided into inches and fractions of an inch. Long objects, such as steam pipes, shaft lines, buildings, etc., are usually measured with a steel tape (Fig. 4). For ordinary purposes tape measures are made of various materials, such as linen braid or steel ribbon, in different lengths, and are graduated either in eighths or sixteenths of an inch. The graduations are printed on the braid, and the better grades are woven with wire selvages or edges to prevent stretching. Spring-tempered steelribbon tapes on which the graduations are accurately etched are to be preferred for extremely careful measurements. They are very convenient in measuring curvilinear or irregular surfaces, as is done in measuring the circumference of a gas tank, the length of a belt to run over pulleys, or the length of band iron around a packing case. When using a tape measure for any considerable distance, care should be taken to see that the tape is supported at frequent intervals or rests on the floor. Otherwise an error will occur, due to the sagging and stretching of the unsupported tape.
Fig. 2. - A Machinist's Rule.
Fig. 3. - Folding Rule.
Fig. 4. - Steel Tape.
Compass-like devices with curved legs, called calipers, are used to measure the diameters of round bodies (Figs. 5 and 6).