Johnson Level & Tool Mfg. 40-6902 - Manual (Page 6)

6 ©2009 Johnson Level & Tool
In the illustration above, 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’).
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.
With an adjusting screw “A” facing to the right of the bubble and with
telescope directly in line with two of the three leveling screws, note
to which side the bubble is off. If to the left, loosen screw “B” and
tighten screw “A” very slightly to remove ONE-HALF the error.
Remove the other half of the error with the two level screws in line
with the telescope. If the bubble is still not exactly centered, repeat
the procedure. If bubble is off to the right, loosen screw “A” and
tighten screw “B”. Otherwise the procedure is identical.
2594H 7/29/09 10:12 AM Page 6