actual circumference of the pipe. This is extremely
important when you are measuring a large diameter
Hold the rule or tape as shown in figure 2-6. Take
the reading, using the 2-inch graduation, for example,
as the reference point. In this case the correct reading is
found by subtracting 2 inches from the actual reading.
In this way the first 2 inches of the tape, serving as a
handle, will enable you to hold the tape securely.
For an inside measurement such as the inside of a
box, a folding rule that incorporates a 6- or 7-inch
sliding extension is one of the best measuring tools. To
take the inside measurement, first unfold the folding
rule to the approximate dimension. Then, extend the
end of the rule and read the length that it extends,
adding the length of the extension to the length on the
main body of the rule. See figure 2-7. In this illustration
the length of the main body of the rule is 13 inches, and
the extension is pulled out 3 3/16 inches; the total inside
dimension being measured is 16 3/16 inches.
Notice in the circled inset in figure 2-8 that the
hook at the end of the particular rule shown is attached
to the rule so that it is free to move slightly. When an
outside dimension is taken by hooking the end of the
rule over an edge, the hook will move to locate the end
of the rule even with the surface from which the
measurement is being taken. By being free to move, the
hook will retract toward the end of the rule when an
inside dimension is taken. To measure an inside
dimension using a tape rule, extend the rule between the
surfaces as shown, take a reading at the point on the
scale where the rule enters the case, and add 2 inches.
The 2 inches are the length of the case. The total is the
inside dimension being taken.
To measure an outside dimension using a tape rule,
hook the rule over the edge of the stock. Pull the tape
out until it projects far enough from the case to permit
measuring the required distance. The hook at the end of
the rule is designed so that it will locate the end of the
rule at the surface from which the measurement is being
taken. When taking a measurement of length, hold the
tape parallel to the lengthwise edge. For measuring
widths, the tape should be at right angles to the
lengthwise edge. Read the dimension of the rule exactly
at the edge of the piece being measured.
It may not always be possible to hook the end of the
tape over the edge of stock being measured. In this case
it may be necessary to butt the end of the tape against
another surface or to hold the rule at a starting point
from which a measurement is to be taken.
Figure 2-6.Measuring the circumference of a pipe with a
Figure 2-7.Using a folding rule to measure an inside
Figure 2-8.Measuring an inside dimension with a tape rule.