Types and Uses - Continued

TM 9-243 TYPES AND USES - Continued TRAMMELS The trammel measures distances beyond the range of calipers. The instrument consists of a rod or beam (1) to which trams (2) are clamped. The trams (2) carry chucks (3). The trammel can also be used as a divider by changing the points. READING A VERNIER CALIPER To read a vernier caliper, you must be able to under- rule (1) is graduated in 0.025 of an inch. Every fourth division (2) (representing a tenth of an inch) is num- stand both the steel rule and vernier scales. The steel bered. The vernier scale (3) is divided into 25 parts and num- bered 0, 5, 10, 15, 20, and 25. These 25 parts are equal to 24 parts on the steel rule (1). The difference between the width of one of the 25 spaces on the vernier scale (3) and one of the 24 spaces on the steel rule (1) is 1/1000 of an inch. Read the measurement as shown above. Read the number of whole inches on the top scale (1) to the left of the vernier zero index (4) and record . . . . . . . . . . . . . . . . . 1.000 inch zero index (4) and record Read the number of tenths (5) . . . . . . . . . . . .0.400 inch Read the number of twenty-fifths (6) to the left of the vernier between the tenths mark(5) and the zero index (4) and record . . . . . . . . . . . . . . . . .3 x .025 = .075 inch Read the highest line on the vernier scale (3) which lines up with the lines on the top scale (7) and record. (Remember 1/25 = .001 inch) . . . . . . . . . . 11/25 or 0.011 inch TOTAL 1.486 inches 6-4