Originally Posted by ispoke
Actually, you'll need to align the 0" mark with the middle of one rivet, and the 12" mark should fall in the middle of another rivet. If you use the 1" mark, you'll only be measuring stretch across 11" on your ruler, and so you will not accurately detect 1/16" of stretch (in 12") until it's gone too far. In other words, measuring from 1" to 12" on your ruler will fool you into thinking the chain is fine, when in fact it could be stretched too much.
Actually if the end of your measuring device is the 0" mark, it is probably better to measure from the 1" mark to the 13" mark. The 0"/butt end can become damaged, thus giving misleading results, sometimes considerably. But indeed, your main point is correct; you want to measure over the full 12", not 11".