Spectra Precision Survey Pro CE v3.6 User Manual - Manual (Page 333)

Survey Pro Reference Manual
R-176
SD/ZA to HD/VD
&RJR 6'=$ WR +'9' 
The SD/ZA to HD/VD screen will convert a slope distance and zenith
angle to an equivalent horizontal distance and vertical distance.
Slope Dist : is the slope distance to be converted.
Zenith : is the zenith angle to be converted.
HI : is the distance that the total station is above
the ground.
HR : is the length of the rod.
;
Earth Curvature Adjust : When checked, the
computed horizontal distance and vertical
distance will account for the curvature of the
earth and refraction.