How to use a guide line for guidance in Leica iCON 3D

From the 3D run screen tap Tools > Guide line options
Frome the Linework dropdown, chose the file (.geo) that contains linework.
Tap Pick polyline.
Tap on the line to be used as guide line.

(The selected polyline will be highlighted yellow and Save Line dialog box will appear)
From here you can give the line an appropriate name.
(Or select Go to proceed without saving line for future use)

Note: Saved polylines can be accessed from the list at the top of the Guideline Options Screen for future use.
Tap Save and use.

Distance to the selected line is provided in top toolbar and displayed as dotted line in section view.

*This feature is only available when .geo file with linework is loaded.