Is our knowledge of the charm sector correct?

A lot of techniques are used to measure $R_b = \Gamma(Z \to b\overline{b})$/$\Gamma(Z \to q\overline{q})$ and they involve different sources of systematic errors. Nevertheless, charm sector knowledge is one of the largest limitations to R b accuracy apart from the particular method used. Some of the most important techniques to extract R b are examined, and for each of them the largest sources of uncertainties coming from the charm sector are reviewed. New recent results from the charm physics are reported, and their incidence on R b systematics is discussed.