Chapter 4 Measurement
57
numbered every 10 mm. See Figure 4-5. The mea-
surement is determined by counting the number of
millimeters.
• Wipe steel rules with an oily cloth before stor-
ing. This will prevent rust. If the rule is to be
stored for a prolonged period, coat it with
wax or rust preventative.
• Clean the rule with steel wool to keep the
graduations legible.
• Make measurements and tool settings from
the 1″ line (10 mm line on a metric rule) or
other major graduations, rather than from the
end of the rule.
• Store rules separately. Do not throw them in a
drawer with other tools.
• Use the rule with care to protect the ends from
nicks and wear.
• Use the correct rule for the job being done.
4.2 THE MICROMETER CALIPER
A Frenchman, Jean Palmer, devised and
patented a measuring tool that made use of a screw
thread, making it possible to read measurements
quickly and accurately without calculations. It
incorporated a series of engraved lines on the sleeve
and around the thimble. The device, called Systeme
Palmer, is the basis for the modern micrometer
caliper, Figure 4-6.
1 2
1
2
1
16
1
8
1
32
1
64
7
16
11″
16
11″
32
3
32
″
″
Figure 4-4. These are the fractional graduations found on a
rule. Measurements are taken by counting the number of
graduations.
1.0 mm
0.5 mm
44 mm 69 mm
245.5 mm
Figure 4-5. Most metric rules are graduated in millimeters and
half-millimeters. They are available in a variety of sizes.
4.1.3 Care of the Rule
The steel rule is precision-made and, like all
tools, its accuracy depends upon the care it receives.
Here are a few suggestions:
• Use the rule for measurements only. Do not
adjust screws or open paint cans with it. Be
careful not to bend your rule.
• Keep the rule clear of moving machinery.
Never use it to clean metal chips as they form
on the cutting tool. This is extremely danger-
ous and will ruin the rule.
• Avoid laying other tools on the rule.
Figure 4-6. The micrometer caliper, past and present.
A—A drawing of the Systeme Palmer measuring device.
B—These modern micrometer calipers operate on the same
principle as the original 1848 invention.
B
A