Display measurement in real time as I'm dragging object away from specified point


I would like to know when the white square is 4" from the right edge of the gold colored object, as I’m dragging it. https://i.imgur.com/p4iIRez.jpg

7:54, of this video (link), describes how to join the face of an object. How would I undo it, at a later, farther point into the project?


I worked in the metric system, but it is also true for the imperial one.
Type 4 inches and enter.

You draw a new line where you want to break that face.