I bought a TL-CN42. The instructions are vague. I inserted the double toothed end between 2 rivets. The single toothed end then rests on another rivet, BUT if I push down lightly, it will go between rivets. Is it time to replace? This is a 9.5 month old, 10 cog cassette, touring bike with about 2,700 miles, 95% on roads or paved trails.
According to this PDF I found it seems that your chain still has life left in it. It's when the ping drops between the pins that your chain has stretched too much.
This is pretty good: 2700mi is about 4400km which is approaching the expected lifespan of a chain (5000km). I've had decent chains which haven't lasted nearly that long. (Admittedly I do occasionally ride in wet weather.)
(Apologies for getting this messed up earlier.)