Welch Allyn 23120P (PAL) CompacVideo Otoscope - User Manual - Manual (Page 9)

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4. Attach a Welch Allyn (4 mm) speculum, provided with the system,
to the video head by rotating clockwise. The quality of the video
image will deteriorate if other speculum are used.
5. Turn on the power switch on the monitor.
6. Turn the rheostat on the power handle to FULL POWER. For
optimum performance, the Video System should always be used
with the rheostat set on maximum brightness. The electronic
controls within the Video System will automatically optimize the
brightness of the image.
No further adjustments are necessary on the video head. The color and
brightness controls on the video monitor may need to be adjusted to
obtain the best possible picture quality.