Q) How will you find the Index error of a sextant? (May-16)
Ans:- Index error:- When the index bar is set at zero, the plane of the index mirror
and horizon glass are NOT parallel to each other.
How to determine:
During day time, clamp the index bar at zero and holding the sextant vertically,
view the horizon through the telescope.
If the true horizon and its reflection appear in the same line, Index error is not
present.
If they appear displaced vertically, turn the micrometer drum till they are in the
same line.
The micrometer reading then is the index error, which is
on the arc if the micrometer reading is more than zero,
off the arc if it is less than zero.
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