Thank you Michael.

So to place a helper line perpendicular to base line, and beginning (or ending) at the base line, I can add a 3rd temporary anchor line, (or curve), beginning at the intersection spot of the base line and helper line.
And then re-size the helper line, by selecting it near the anchored end, just in case the other end happens to end at a 4th line, (or curve), end.

- Brian