How to unlock a file and finding the perpendicular line on the measuring tool

Hello, and happy holidays
Two questions, occasionally a file is locked and then I have to copy it for a new file in order to open it, otherwise its deleted or locked. The second question, how do I find the perpendicular line when re-sizing objects? The perpendicular line shows up between the axis lines but not easy to find. Its not the red, blue and green lines, but a lavendor colored line. The perpendicular term shows up in the notes while re-sizing an object if its on a separate position other than the red, blue, green axis…