CASSENS & PLATH BOBBY SCHENK Sextant Handhabung Seite 27

BOBBY SCHENK Sextant
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Tilt Error of the Index Mirror
The index mirror must be at right angles to the plane of the instrument.
In order to determine whether the index mirror is perpendicular to the plane of the instrument, the
alidade should be positioned approximately at the centre of the graduated arc. Now look from
direction of the index mirror, passing the inner edge of this mirror, at the zero point of the
graduated arc. Next to this, reflected in the mirror, the opposite end of the graduated arc will
become visible. If the two images are level a), the index mirror is correctly positioned. If the two
images are not level b) the index mirror has to be adjusted by means of the correction screw as
shown in the following illustration.
Smaller differences are tolerable because these errors do not directly affect the measuring
accuracy.
a)
Take the sextant like this
to identify and correct tilt
error of index mirror
b)
Instructions