Each tuner is individually calibrated at the factory, whatever that means. I tuned up my old RG410 with this tuner and distorted barré chords sound good. I haven't touched a dial, only stepped on it. As I only use regular tuning anyway. But yes, it's very easy to use. The only, if any, bad thing about it is that you must remove three (maybe four) screws to change the battery. Then again, if you use it on a pedalboard you probably have it powered up without a battery.
I've met Paul, very bright and nice guy.

Tried his guitars, great stuff!
