Spectra Precision Survey Pro v4.5 Ranger Reference Manual - Manual (Page 129)

Survey Menu – Conventional Mode
R-121
Read Circle : Will read the current horizontal angle from the
instrument and set that as the backsight circle. (Non-zero backsight
circle values are typically used only when surveying in true
azimuths.)
Check Backsight: Once the backsight has been checked by distance
or angle, the symbol will be replaced with a .
By Distance : will take a shot to a prism located over the backsight
point and compare the measured distance with the computed distance
between the occupy and backsight points stored in the current job.
Note: Checking the backsight by shooting a distance does not apply if
the backsight is defined by a direction.
By Angle : when the backsight is defined by a direction, this routine
will read the current horizontal angle from the total station and
compare that to the backsight direction.