Great question, by coincidence (prompted perhaps by reading recent posts) I've been kind of curious about this myself over the last few days.
More specifically, if you built two identical bases, same physical measurements, same woods, etc., would they end up being calibrated differently? I assume your parts tolerances are quite high, so it's a bit puzzling to me why calibration seems to be such a major endeavor.
Not asking for trade secrets, of course, just a little insight.