Spectra Precision Survey Pro v4.6 Recon and Nomad User Manual - Manual (Page 139)

Mapping Plane Scale Factor
129
If you are using a grid scale with sea level correction,
including auto map plane mode, the Apply Scale Factor
wizard will open where a reference point and vertical
distance are needed to compute the scale factor. The
Vertical Distance is the vertical difference from the
reference point to your target. If working on a level
surface, this value will be zero.
When you tap Next, or if your reference point is already
known, you will be presented with the screen shown here
where you can preview and accept the changes. When
you tap Accept, you will return to the original screen and
the Distance Scaled to Grid will replace the input distance
entered in the edit field.