Originally Posted by
TimothyH
The problem with "gray area" is that too many wait for a part to be completely worn out and wind up getting stuck on the side of the road when things break.
That's the purpose of a spec, to prevent people from running stuff down to the point where it breaks.
Virtually all of these instruments err on the safe side. The complaints generally are that they err on the too safe side and result in changing the chain before the "magic" 1% elongation number.
And chains generally don't break for being worn out - they break because they're damaged somehow. So your point is valid for a lot of stuff, but doesn't really apply to chain checkers.
Full disclosure - I use the Park tool - it's really handy. I know the limitations, and I'm fine with them.