Park Tools Chain Checker arrived today. Tried it on my chain, and assumed it wasn’t working, because it suggested my chain was totally wrecked. Tried it on a mate’s chain, and it said his chain was fine. Then thought about it for a minute, remembered that I hadn’t changed my chain for a while, looked up when I last did that, discovered it was in August 2012… whoops. Time for a new chain and cassette, it appears, as I’ve done about 4k miles since the last change.