[Ifeffit] Short questions

Hi Ifeffit people, I have a couple of short questions for you. I used the "Scott Calvin's rule" (number of variables < 2/3*Nip) to calculate the maximum number of allowed free parameters but I read that some people use the Nyquist theorem, which are the differences between them? and, which one is more correct? And finally, how are errors calculated in Artemis for the parameters N (coordination number), deltaE0, S02, deltaR and sigma^2? Thanks a lot JA