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Parallel Motion Protractor (PMP)
Introduction
The PMP is a valuable tool for plotting direction quickly and accurately.
When in restricted waters and plotting fixes every 3 minutes, you will
greatly appreciate this instrument. The PMP is usually anchored to the
top of the chart table.
The PMP is designed to keep the moveable compass rose oriented to the
longitude and latitude of any chart. An arm is attached to the moveable
compass rose which can be rotated to whatever bearing you require and
then moved to the object on the chart that the bearing was taken to, so
an LOP can be drawn.
Part
Description of function
Anchor plate
Allows the PMP to be attached to the chart table.
Friction control knob
Allows adjustment of movement of the arms at the
two linkage points.
Bearing scale
A 360° circle marked in 1° increments. When
locked it will maintain its orientation when moved
around the chart table.
Index marks
Used to align the ruler on the desired bearing. The
four marks spaced every 90° are inscribed on a
plate that is directly linked to the handle and the
ruler.
Protractor lock switch
Locks the bearing scale when aligning the PMP.
Scale lock switch
Locks the PMP ruler on a desired bearing.
Figure 2-15. Parts of a PMP.
2-26
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