Nikon DTM-502 Series Instruction Manual page 164

4-4. Zero Point Errors of Vertical Scale and
Horizontal Angle Corrections
1) Checking
(1) Set up the instrument on the tripod and complete the leveling procedure
described in [2-5. Leveling] section. (See p.2-10)
(2) On the BMS, with the telescope in its Face1 position, sight a target that is
placed within ±45° from the horizontal plane, and read the vertical angle
(VA1).
(3) Rotate the instrument and flip the telescope to its Face2 position, and take
another vertical angle reading (VA2) to the target.
(4) For the Vertical angle "Zenith" setting, if the "VA1+VA2" equals 360°, then
the adjustment is not necessary. For the Vertical angle "Horizon", when the
"VA1 + VA2" is 180° or 540°, then the adjustment is not required either.
• Difference in vertical angle reading from 360° (for Zenith), 180° or 540° (for
Horizon), is called the Altitude constant. When your instrument is out of
tolerance, perform the Calibration program and adjust it before starting your
fieldwork.
4
4-3