Nikon DTM-502 Series Instruction Manual page 169

4-5. Instrument Constant
The instrument constant is a numerical value used to automatically correct for the
displacement between the mechanical and electrical centers when measuring
distances. Although this adjustment was made at the time of delivery, it is
recommended that the constant be checked several times a year to ensure the
highest operational accuracy. Checks can be performed by either comparing a
correctly measured base line with the distance as measured by the EDM, or by
using the following procedure.
(1) Perform the check on as flat an area as possible. Set up the DTM-502 at
Point P, with the reflector prism 100m away at Point Q (taking the prism
constant into account).
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(2) Measure the distance between Points P and Q and note it for future reference.
(3) Set up another tripod between the two, at Point R, and transfer the DTM-502
to it. Install a reflector prism back on the tripod at Point P.
(4) Measure the distances to Points P and Q. Check that their sum falls within
the allowable range of error from the distance measured in Step (2).
PR+QR=PQ
(5) Move the DTM-502 to other points along the line PQ, and repeat Step (4)
several times. Calculate the average.
(6) If the difference between the value of PR+QR and the value PQ is 3mm or
longer, contact your nearest Nikon representative.
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P
About 100m
P
Q
R Q