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Unit 2 Reading Rulers
179
graduations are the next longest, the 1/4-inch graduations are next, then the 1/8-inch
graduations, and so forth.
1
64
32
2
1
2
1
4
1
8
1
16
1
32
1
64
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When reading any measurement, with a ruler or otherwise, fractions should be
reduced to their lowest terms. If you measure 12/16″, it is written or read as 3/4″.
Reading a Decimal Ruler
In the machine shop, more work is done in decimal inches than in common fractional
inches. That is, the inches are divided into decimal fractions. A decimal-inch ruler
normally has graduations of 1/10″ along one edge and 1/50″ along the other edge.
Graduations of 1/100″ are too tightly spaced together to read accurately, so other
instruments are used to measure hundredths of an inch or less.
1
50
10
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
2
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
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The Metric System
The metric system of measurements has evolved over the last few centruries. In 1960,
the metric system was offi cially named Système International d'Unités (or SI for
short.) Today all industrialized nations except the United States use the metric system.
Products that are made or serviced in the United States are often exported through-
out the world, so it is important for an American machinist to be able to use the
metric system.
Length measurements in the metric system are based on the meter. A meter is
just over 3 inches longer than a yard.
The metric system uses powers of 10 to signify numbers that are too large or
too small to be practical for use. These numbers are written with a Greek or Latin
prefi x to signify what power of 10 the base number is multiplied by. It is common
in writing large metric numbers to leave a space after every third place, rather than
a comma.