A while ago I posted wondering about the validity of a Park chain checker in relation to two of my chains. One is pretty old>12yrs and the other is pretty new<2yrs. The new one wore out quickly according to the checker. I didn't believe it and posted wanting some advice. Well the chain was shot, got a new one , found my cassette was shot also.Went to the LBS got a new 14-34Shimano to replace my 13-34 Sun Race. All is good now. My point is... I do believe chain checkers work if even to only warn you of possible problems. I wish I had gotten one sooner.

I have one and usually check its result against a tape measure. Anything over 12 inches... well...