ruler_doc.txt

Note: This tool only works on SOP geometry currently (you must be in a SOP context. 
Click and drag on the currently displayed geometry to draw out a measurement on it. The measurement represents the distance between the point on the geometry initially clicked on and the point currently being hovered on. 
Multiple measurements can be drawn out. They will persist in the viewport until a new state is entered, at which point they will be destroyed. The only states that are an exception to this are the selection state and the view state. This allows you to continue to tumble around while still putting down measurements.
Press the Undo hotkey to remove a measurement (default is 'z').
Press the Copy to Clipboard hotkey to copy the most recent measurement to the clipboard (default is 'q').
Press the Pop Copy hotkey to copy to clipboard and remove the most recent measurement (default is 'f').
The state will respect point snapping if it is currently enabled.
The state will intersect against one of the principle planes (the xy, xz, and yz planes) if no geometry is underneath the cursor.
Angle snapping can be enabled by holding down Ctrl while dragging. This will find the angle between the vector of the current measurement and the most reasonable axis, based on the current view, if the measurement were to be projected onto the most reasonable principle plane that contains that axis. It will then take that angle, and snap it to the closest multiple of 15, in degrees.