Originally Posted by
scottp20
I measured it but in cm only have a 6inch ruler, I got 8 pins in 9cm including the first one it was very very slightly more than 9cm from the center of the first and last maybe 0.5mm more
You have
6" ruler, and a
1/2" pitch chain, why are you measuring anything in
cm? Nothing wrong with the metric system, but here's an example where using inches makes infinitely more sense. If you can't find an inch ruler, calculate how many cm in 6" (152.4mm) and compare the stretch over 12 links to that, with the pass/fail line at 0.8mm, or 153mm total.
BTW even if it's borderline, it's better to replace the chain anytime you replace a cassette because a worn chain will rapidly wear a cassette to match it's condition.