Originally Posted by
WallbrownF
..I figured that it would be best to measure it loose and not stretched...
I'd be more concerned about measuring between the right spots than stretch errors. A standard, 2.0 mm spoke really won't stretch that much.
The big advantage of measuring a loose spoke is that it makes "inside elbow" and "end-of-spoke" much more defined spots, and you'll have a straight run between them.
Another concern, particularly on an older wheel/bike, is previous history/quality of repairs. Worked on a wheel that didn't make sense until I figured out that it had 3 spokes of two other lengths lurking among the others on one side.