Stringtech's Compensated nut....

[sgosnell]

I tune at the 5th fret, because that's close to where I play most of the time. But there are lots of methods for tuning. I will say that when changing strings, I tune the open strings, stretch them, retune, then go to the 5th fret for final tweaking. That's just what works for me.

[RJVB]

With a correctly built and set up guitar there shouldn't be much noticeable error with either approach and during normal playing. Since installing the ZeroGlide on my archtop, for instance, I'll maybe get a 1-2 ct error on the open string or at the 5th fret depending on where I tune. That's good enough given how easy it is to pull or push a string sharp while playing.