This ruler was added in version 17.01.06.
Isometric projection is a method for visually representing three-dimensional objects in two dimensions in technical and engineering drawings. It is often used in game art.
This mode will help you draw isometric art. It has 3 rulers for which you can change the angles.
The Line Select Mode parameter determines which ruler is chosen when you draw:
When Box Mode is enabled, your pen position will be clamped to a 3d bounding box while you draw, helping you quickly close boxes without overshooting. The dimensions of the box are determined automatically one at a time as you first draw on each axis. The dimensions are reset when you lift the pen.
While not drawing, holding the control key will also display the angle control points, the measure point unit distance control point, and the freeze mode toggle control point.
Clicking on the Freeze Mode control point (or pressing the associated keyboard shortcut) will create a fixed frame of reference at your pen position. You can use this and the measure points to accurately subdivide sections.