If a straight line segment is selected, its length may be changed by entering a new value in the upper right command window. However sometimes the changed line keeps one end at the same point, other times both ends move.
Is there some way to keep one end anchored?

- Brian

If the line to be re-sized, begins or ends at the end of a second line, (or curve), the re-sized line is "anchored" at said intersection.

Tested...

It seems, when a line is moved to anchor on an end point of another line (or polyline), then the resize keeps this anchor point and the line resizing uses this anchor as fixed point.

This is my empirical observation.
Michael will give us the right rule, I presume...

FR

Hi Phiro,
I believe that you are correct. The "anchor" can also be a curve end. (At least in 2D...)

- Brian

The "anchor" curve can be trimmed by the line, and even (re) joined, to preserve an anchor.

Hi Brian, yes if it's a line or arc being resized it will look through other open curves and if there is one that has a shared endpoint with the one being resized it will use the shared endpoint as the scale origin. If each end is touching something else it will target the end that was nearest to the selection click point.

Otherwise if there isn't any other curve touching it, it will use the midpoint as the scale origin.

- Michael

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