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©2009 Johnson Level & Tool
In the illustration to the right, the index
has passed the 44 degree line but has
not gone as far as the 45 degree line.
In this case, the third vernier line from
the index is lined up with one of the
lines on the circle. Since each vernier
line represents 15 minutes add 45 minutes to the 44 degree reading
(3 times 15 minutes equals 45 minutes). Therefore our exact reading
is 44 degrees, 45 minutes (44º45’).
The Vertical Vernier.
In reading the vertical vernier, the principle is exactly the same as the
horizontal vernier. Note however, that the vernier is below the circle
portion rather than inside as in the case of the horizontal. One other
minor difference is that you will read angles up or down rather than
left or right. Here again is a double vernier. The right hand side
reads angles of elevation (up) and the left hand side reads angles of
declination (down). These are the only differences between the
horizontal and vertical verniers.
5. Calibration
5.1 Bubble adjustment
If the telescope bubble does not
remain centered after having
leveled the instrument, and
reversed the telescope end for
end (180º) (as described under the Leveling section) the need for
adjustment is indicated. Use a 3mm hex key.
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