A measurement of R-b using five mutually exclusive hemisphere tags has
been performed by ALEPH using the full LEP1 statistics. Three tags ar
e designed to select the decay of the Z(0) to b quarks, while the rema
ining two select Z(0) decays to c and light quarks, and are used to me
asure the tagging efficiencies. The result, R-b = 0.2159 +/- 0.0009(st
at) +/-0.0011(syst), is in agreement with the electroweak theory predi
ction of 0.2158 +/- 0.0003. (C) 1997 Published by Elsevier Science B.V
.