Correct.
The datum ( zero or "0" line) of those measurements is the front of the dashboard horizontally and some other reference (top of frame? - don't have it in front of me right now) vertically, but subtracting one from the other gives you the distance between them. Getting a good reference from the front of the dashboard is a little iffy, especially down lower on the body where the toe panel cuts back from the plane of the dashboard.
BTW, the symbols like 0 with a slash and others ARE Greek.
c with a line stands for centerline.
