(6) Ring adjuster. The knob at the upper right side
is used for fine rotation adjustment of the vernier scale.
(7) Disk adjuster. The knob at ninety degrees left
of the zero on the vernier dial is used for fine rotation of
the inner protractor dial.
b. Use. The following steps outline the procedures for
measuring the angle of a control surface in an extreme
(1) Align the control surface in the neutral position.
(2) Lock the ring to the disk at zero by dropping the
lockpin in the deepest slot.
(3) Place the protractor in the approximate middle
of the control surface next to a rib.
(4) Using the ring adjusting screw, turn the ring to
center the bubble in the level, as shown in figure 7-2.
(5) Lock the ring to the frame with the ring-to-frame
(6) Move the control surface to an extreme limit of
(7) Unlock the disk from the ring with the disk-to-
(8) Turn the disk adjusting screw until the bubble is
centered in the level, as shown in figure 7-3.
(9) Read the control surface throw in degrees.
The angle is read by reading the degrees on
the inner dial that correspond to the zero on
the vernier scale. The vernier scale
indicates tenths of a degree.
c. Care. Observe the following practices for the care
and upkeep of protractors:
instruments. Do not drop or otherwise mistreat
protractors, because some damage may render them
(2) Store protractors in protective boxes.
Figure 7-2. Setting Protractor with Flight Control Surface in Neutral Position