Yep.....it was in one of those links I provided for you to read.
Couldn't find the detailed sketch I know is in the SSM.
This picture shows new on top and a used chain on the bottom.
And he's measuring the stretch over about 14", not the required 21 pin measurement.
So, stretch out the chain like shown, and it would be good to stretch it a bit. One end on a nail, the other with a bungee cord, weight, whatever. count off 21 pins, measure from center to center, but left edge of the pin to left edge is the same.
127mm or 5" is brand new.
service limit is 128.9mm or 5.075"
While you got it in your hand, check for any stiff links.
I'd replace it if you have any.
http://www.ls-650.de/techfotos/steuerketten.jpg