c. Mount the new scale-mask assembly on the shaft and center
the 4000-25000 RPM window in the dial over the white panel segment
beneath the dial.
a. Tighten both setscrews securely.
4.7.4 D I A L
To replace the dial:
a. Remove the instrument from the case.
b. Set the range switch to the 4000-25000 RPM position and re -
move the scale -mask assembly (refer to paragraph 4.7.3, steps a and b).
c. Note the approximate dial setting and remove the dial from
the potentiometer shaft without turning the shaft. To remove the dial,
loosen the two setscrews in the dial hub under the instrument panel.
d., Mount the new dial at the approximate setting noted in step
c. Tighten one setscrew in the dial hub.
The dial should not rub against the panel when rotated; allow
for a minimum clearance of 1/16 -inch.
e. Rotate the dial from the limit stop in one direction to the limit
stop in the other direction. Note the distance between the red marker
and both ends of the 4000-25000 RPM scale. (The ends of the scale
should travel approximately 1/4-inch beyond the red marker.) Adjust
the dial until the red marker is equidistant from both ends of the scale.
f. Tighten both setscrews in the dial hub.
g. Mount the scale-mask assembly (paragraph 4.7.3, steps c and
d,) and mount the instrument in the case.
h. Calibrate the stroboscope before making speed measurements.