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E. Electronic Distance: Combined Constant
1. Combined Constant
An EDM distance is the sum of the measured distance and the instrument and reflector constants, Figure E-1.
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| Figure E-1 Instrument and Reflector Constants |
| D = D'+(CI+CP) | Equation E-1 | |
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D: corrected distance |
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k is the Combined Constant. Because it is internal, most instruments compensate for CI. The surveyor needs only to input the reflector constant; typical values are 0 mm and 30 mm. Over time the TSI may lose calibration and rough reflector handling require determination of a new constant to use.