Originally Posted by
Scrodzilla
Chain "stretch" doesn't occur by the side plates actually stretching, but rather the pivots and bushings becoming worn (think of a donut with a hole that keeps getting bigger over time) - which makes the chain get longer. Using a ruler isn't really as effective as a chain wear indicator.
If you take apart a worn chain you will see that the pins develop grooves where the inner plates sit. this wear over the length of the chain causes "stretch". Both systems for checking seem to work just fine as I have compared a little on peoples' worn chains at the co-op. If you look in the Mechanics forum it seems like most arguments are against chain checkers
fwiw, using the ruler to check wear got me three chains to last cassette. unfortunately I don't have miles logged