CHAPTER 2
MEASURING TOOLS AND TECHNIQUES
When performing maintenance and repair tasks on
catapults and arresting gear equipment, you must take
accurate measurements during inspection, to determine
the amount of wear or service life remaining on a
particular item or to make sure replacement parts used
to repair equipment meet established specifications.
The accuracy of these measurements, often affecting
the performance and failure rates of the concerned
equipment, depends on the measuring tool you use and
your ability to use it correctly.
COMMON MEASURING TOOLS
LEARNING OBJECTIVES: Identify the
different types of measuring tools. Describe
the uses of different types of measuring tools.
Describe the proper care of measuring tools.
You will use many different types of measuring
tools in the daily performance of your duties. Where
exact measurements are required, use a micrometer
caliper (mike). If you use the micrometer caliper
properly, it will allow you to measure within one
ten-thousandth (0.0001) of an inch accuracy. On the
other hand, where accuracy is not extremely critical, a
common straightedge rule or tape rule will suffice for
most measurements.
RULES AND TAPES
Figure 2-1 illustrates some of the commonly used
straightedge and tape rules. Of all measuring tools, the
simplest and most common is the steel or wooden
straightedge rule. This rule is usually 6 or 12 inches
long, although other lengths are available. Steel rules
may be flexible or nonflexible, but the thinner the rule
is, the easier it is to measure accurately with it, because
the division marks are closer to the work to be
measured.
Generally, a rule has four sets of graduated division
marks, one on each edge of each side of the rule. The
longest lines represent the inch marks. On one edge,
each inch is divided into 8 equal spaces, so each space
represents 1/8 inch. The other edge of this side is
divided into sixteenths. The 1/4-inch and 1/2-inch
marks are commonly made longer than the smaller
division
marks
to
facilitate
counting,
but
the
graduations are not normally numbered individually, as
they are sufficiently far apart to be counted without
difficulty. The opposite side of the rule is similarly
divided into 32 and 64 spaces per inch, and it is
common practice to number every fourth division for
easier reading.
There are many variations of the common rule.
Sometimes the graduations are on one side only,
sometimes a set of graduations is added across one end
for measuring in narrow spaces, and sometimes only
the first inch is divided into 64ths, with the remaining
inches divided into 32nds and 16ths.
Steel tapes are made from 6 to about 300 feet in
length. The shorter lengths are frequently made with a
curved cross section so that they are flexible enough to
roll up, but remain rigid when extended. Long, flat
tapes require support over their full length when
measuring, or the natural sag will cause an error in
reading.
MEASURING PROCEDURES
To take a measurement with a common rule, hold
the rule with its edge on the surface of the object being
measured. This will eliminate parallax and other errors
that might result because of the thickness of the rule.
Read the measurement at the graduation that coincides
with the distance to be measured, and state it as being so
2-1
Figure 2-1.—Some common types of rules.
