Spectra Precision Focus 30, User Manual

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4 Setup
64 Spectra Precision FOCUS 30 User Guide
When the Spectra Precision Survey Pro is running, the software has additional func-
tions that reduce the bottom mark measurement to the required vertical instrument
height to the trunnion axis, see
Figure 4-53 and the following paragraph.
Fig. 4-53 Instrument height measurement
0.158m
(0.518ft)
Hm
Hc
Ih
The measured distance (Hm) is corrected for the slope of the measurement to obtain a
vertical measurement to the bottom mark (Hc). The constant from the bottom mark to
the top mark (0.158 m/0.518 ft) is added to the Hc to obtain the vertical instrument
height from the ground mark to the trunnion axis (Ih). For more information, refer to
the Spectra Precision Survey Pro documentation.
Alternatively, to obtain an accurate measurement to the top mark (Ih), you can manu-
ally measure the slope distance from the ground to the bottom mark (Hm). To calcu-
late the total instrument height (Ih), insert the measured slope distance (Hm) into the
formula below: