Spectra Precision Survey Pro v4.5 Recon and Nomad Reference Manual - Manual (Page 127)

Survey Menu
R-119
Backsight Circle
Survey Backsight Setup Circle… .
The Backsight Circle dialog box is used to modify the horizontal angle
read from a total station so that the resulting angle is an azimuth.
This routine can also be performed from the Backsight Solved screen.
Backsight Circle: is the angle that will be subtracted from all
horizontal angles read from the total station or entered manually
when data collecting in manual mode.
Set : Sets the value entered in the Backsight Circle field as the
backsight circle and returns to the previous screen.
Note: Closing this dialog box without tapping the Set button will
result in no changes made to the original backsight circle.
Read from Instrument : Reads the current horizontal angle from the
total station and puts that value in the Backsight Circle field where it
can then be Set as the backsight circle. This is typically performed
when it is known that the total station is facing a direction with a
zero azimuth.