I remember reading somewhere that it isn't accurate. Just tried it on a chain that I got about a month ago and it says it's worn out. The chain was a make I haven't heard of so maybe was very poor quality.
Well the design of most chain checkers is nigh on exactly the same so you would think they'd all do what they are designed for or it would be well talked about.
Can't vouch that the park tool does indeed show the 0.75 or 1.00 it states it does in terms of stretch though.
Mines good and will save me a fortune in related knackered parts - see my usual chain swap, closely followed by rear cassette and usually middle ring.
I've got one - it's doesn't fit in when the chains new, fit's in the 0.75% side after a while, then the 1% at bit later. Not sure how accurate it is but I try and follow it's guidance 🙂
I like the CC-3 better.
I got the CC-3 and works great 🙂
depending on your mileage a new chain won't last long on worn chainrings,,,