The partial decay width of the Z to b (b) over bar quark pairs has been measured by the DELPHI detector at LEP. b-hadrons, containing b-quarks, were tagged by leptons with high transverse momentum relative to the hadron or by tracks with large impact parameters to the primary vertex. The ratio of the numbers of events with a single such tag to those with two tags was used to estimate the efficiency of the method and to reduce the systematic uncertainty. Combining all methods, the value: [GRAPHICS] was found, where the third error corresponds to a +/-8% uncertainty on the c (c) over bar production width. A maximum likelihood fit to the single and di-lepton distributions gave the branching fraction of the decays of b-quarks to leptons as: [GRAPHICS]
