Improved Measurement of Rb,Rc at SLD 
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We present a preliminary measurement of the Z0 boson to b and c quark 
production fractions Rb and Rc, using the 96-98 SLD data sample of 400K 
hadronic Z0 decays. We extract Rb and Rc simultaneously using a multi-tag 
method. This measurements relies on the unique features of the SLD 
experiment, the high resolution CCD vertex detector and the micron size 
beam spot. This analysis uses improved tagging algorithms and most of the 
tagging efficiencies are measured from data to reduce systematic errors.