When the Rulers button is on, rulers can be created by clicking twice at the endpoints of the ruler, or by pressing and dragging, where the ruler will extend from the press and release points. The ruler will only be visible in the window where the first button press occurred, and only rulers in the main window will be visible in hard copies.
Rulers remain visible until another cell is edited, or until deleted. The rulers in effect for a certain cell are remembered, so that upon returning to a previously edited cell, the rulers previously in effect will be visible.
Rulers can be deleted, while the Rulers button is on, by pressing the Delete or Tab (undo) keys, and are deleted in reverse order of creation. Rulers associated with the current cell can be deleted at any time with the !dr command.
When a ruler is being created, the ghost-drawn vector which appears when creating a ruler indicates the side which will have the gradations. The side with the gradations can be toggled by pressing the `/' or ` \' keys.
If Shift is pressed during completion of a ruler, the endpoint will be the start point of a new ruler, and the calibration in the new ruler will be an extension of that in the current ruler. Thus rulers can be ``chained'' around an object to measure the periphery.
If Constrain 45 button in the Edit Menu is active, the angle is constrained to multiples of 45 degrees. If not set, the angle is unconstrained, but snaps to multiples of 45 degrees when the angle is close. In either case, pressing the Ctrl key removes the constraint.
The endpoints initially do not snap to grid points, unless the RulerSnapToGrid variable is set. The period (`.') key toggles snapping to grid points while in the Ruler command.