Sorry, I'm still not understanding about the half step. If you want accurate intonation, you're going to need a chromatic tuner that can tell you exactly how sharp or flat a note is. For example, tune the open G string using the tuner then play the G at the 12th fret and see how many cents sharp/flat that note is from the G an octave up from the open string. I would expect that to be a small number of cents, perhaps 5-20. Then you can adjust the screws to compensate.
A "half step" is 100 cents, the difference between G and G#, for example. That would be an insanely bad intonation and probably grounds for a refund. I doubt that's what you're dealing with, but it can happen. I've had it happen exactly once.