Plotting lstruments, Continued
Tools of the
Compasses: Compasses are not to be confused with the direction
Trade, continued finding compass such as the magnetic or gyrocompass. The compasses
referred to here are tools that are very similar in appearance to the
divider. The distinction between dividers and compasses is that while
both divider legs are fitted with needles, the compass legs are fitted with
a needle on one leg and a marking lead or pencil on the other.
Compasses are useful for
scribing circles and arcs such
as radar ranges or perhaps
showing the limits of a lights
visibility. Dividers and
compasses (fig. 8-8) will give
best results when the
adjustment screw at the hinged
end is kept tight enough to
permit ready use but prevent
slippage. The needle points
should be sharp, extended to
the same length, and locked
securely using the locking
Figure 8-8. Compass and dividers.
A variation of the compass, called a beam compass, is used when a
greater spread is required than an ordinary compass can accommodate.
The beam compass is simply a long bar with a needle point at one end
and a marking lead or pencil at the other end; both are adjustable. This
compass is very useful when using large-scale charts such as harbor
Dividers: A pair of dividers is an instrument or tool used to measure
the difference between two given points. It consists of two small pieces
of metal, plastic, or wood, hinged at one end, allowing the opposite ends
to be separated. There are needles or points placed in the ends of both
legs which enable the user to obtain a more accurate measurement and
allow the tool to be swung from one length to another without slipping.
There are many sizes of dividers, but the 5- and 6-inch sizes have been
found to be the most popular and useful. Larger dividers are handy at
times, but can be clumsy to use.