Snap Guides

Snap Guides are temporary lines and arcs that appear along existing elements, to assist accurate element placement.
Press Shift during input
From the context menu, use Lock to Guide Line/Snap Guide
Use the Snap Guides command in the toolbar dropdown
Use View > Snap Guides
Click Q on any edge or point to “Force Snap Reference”, to highlight an edge or node as a Snap Reference instantly (regardless of the timer set in the Work Environment).
Note: The predefined Shortcut for this command is the Q key, but may vary depending on your localized version of ARCHICAD.
Snap Guides relative to any Snap References you have marked, and to the relations among those Snap References.
From the context menu during element input, use the Place Snap Guide/Snap Circle command:
During Tracker input, click the crosshair icon in the coordinate field. The edited element will then jump to that coordinate value and the applicable Snap Guides will appear.
Options for Snap Guides/References are set at: Options > Work Environment > Input Constraints and Guides.