One more point. The ruler method to check for elongation is the best, but it is not always wise with Campy chains. A well-maintained Campy chain elongates so little that the length may be fine, but the roller can be shot and the side clearance excessive. I've measured .2% elongation after 6,000 miles, but the roller spacing increased from .200 inch to .240 and the side clearance was nearly twice the original amount, at .013 inch. That chain was shot and also wore my 19T cog enough that it skipped with a new chain. The .5% elongation rule does not work with Campy chains.