Most chain wear measuring tools add roller wear to the elongation and can report a new chain to be stretched by .25%. This initial false wear must be subtracted from future readings. Even then, the tool can report twice the acutal elongation, since roller wear is much larger than the amount of wear on the pins and innerplate bushings.
Campy chain elongate so little (if properly maintained), that the rollers can be extremely worn, but the chain will measure little elongation with a scale, so the scale method is not reliable for a Campy chain. I use calipers to meaure roller spacing and toss the chain when the roller spacing increase by .035-.040 inch.