Measurements of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="italic">R</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">b</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>with impact parameters and displaced vertices

We present measurements of ${\mathit{R}}_{\mathit{b}}$ using the SLD at the SLC. The analyses use 2D and 3D impact parameter tags and a displaced 3D vertex tag which all exploit the small size and stability of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ interaction point and the precision 3D CCD pixel vertex detector to achieve high bb\ifmmode\bar\else\textasciimacron\fi{}-tagging efficiencies and purities. The combined measurement yields ${\mathit{R}}_{\mathit{b}}$=0.229\ifmmode\pm\else\textpm\fi{}0.011 and is consistent with standard model predictions. \textcopyright{} 1996 The American Physical Society.