like the man said, throw the chain checker away, get a steel ruler...

someone telling you to replace a chain 'immediately' is jerking you around and trying to force a sale based on 'fear.'

it's a CHAIN...if it's worn out and you ride it another 50, 100, 150, 200 miles, nothing is going to explode or cause grave damage to the drivetrain.

I've never had to change a cassette out because a chain was excessively worn. yeah, it CAN happen, but there's no hard and fast rule about it...

if you install a new chain and it shifts ok, you're good to go.

shifts like crap, well...that's a good sign that other parts are probably hosed.