A precision rule placed on the edge of one pin completely covers the pin at the opposite end. As the chain elongates, the covered pin is exposed. It's easy to see the exposure of 1/2 the pin, with adequate accuracy. Brandt contends that 1% or the entire diameter of the pin being exposed is the limit. If the full length is measured, .5% is just over 1/4 inch. If you can't see that with a tape measure, you're blind.
I'm also seeing the minimal elongation with the new SRAM AXS chains. Users are report very high mileage with little elongation. They'll find out the hard way that they should have used a rotation or changed their chains sooner, when they get new-chain skip.
As for Campy's recommendation, that measurement is mostly roller wear and little elongation over that short length. The roller hole wears far more than the OD.