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35. CHECKS AND ADJUSTMENTS
7. Replace the optical plummet reticle cover by
matching the grooves on the cover with the
grooves on the optical plummet.
The additive distance constant K of the GM is adjusted to 0 before delivery. Although it almost never deviates,
use a baseline with a known distance precision to check that the additive distance constant K is close to 0
several times a year and whenever the values measured by the instrument begin to deviate by a consistent
amount. Perform these checks as follows.
• Errors in setting up the instrument and reflective prism or in sighting the target will influence the additive
distance constant. Be extremely careful to prevent such errors when performing these procedures.
• Set up so that the instrument height and the target height are identical. If a flat place is not available, use an
automatic level to make sure the heights are identical.
PROCEDURE Checking
1. Find an area of flat ground where two points 100 m apart
can be selected.
Set up the Instrument at point A and the reflective prism at
point B. Establish a point C half way between points A and B.
2. Precisely measure the horizontal distance between point A
and point B 10 times and calculate the average value.
3. Place the GM at point C directly between points A and B
and set up the reflective prism at point A.
4. Precisely measure the horizontal distances CA and CB 10
times each and calculate the average value for each
distance.
5. Calculate the additive distance constant K as follows.
K = AB - (CA+CB)
6. Repeat steps 1 to 5 two or three times.
If the additive distance constant K is within ±3 mm even
once, adjustment is unnecessary.
If it always exceeds this range, have our service
representative perform an adjustment.
35.6 Additive Distance Constant
Groove
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