It's the percentage of subcomponents that are totally ready for the next process, when the next process is ready for them. I found it pretty good as you can get the product of all the separate processes that gives you the overall C&A for the whole VSM.
So
Process 1 = 60% Process 2 = 70% Process 3 = 80%
(0.6 x 0.7 x 0.8) x 100= 33.6% %C&A
So the overall Value stream is 33% complete and accurate.
Linky is awesome, you only get 2000 clicks a month free but I would imagine that will be more than enough.
Also if you feel like setting up your own there's
Which has a docker image and you can set up on Amazon aws under their free scheme, if you want to go that route give me a shout