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
understand both the steel rule and vernier scales. The
steel rule (1) is graduated in 0.025 of an inch. Every
fourth division (2) (representing a tenth of an inch) is
numbered.
The vernier scale (3) is divided into 25 parts and
numbered 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
Read the number of tenths (5)
to the left of the vernier
zero index (4) and record................... 0.400 inch
Read the number of twenty-fifths (6)
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 or0.011 inch
TOTAL
1.486 inches
6-4
