Measurement of $\mid V_{cs} \mid$ using W decays at LEP2

Decays of $W^{\pm}$ bosons, produced at LEP2, have been used to measure the $|V_{cs}|$ element of the Cabibbo-Kobayashi-Maskawa matrix. Values for $|V_{cs}|$ were extracted both from the measured hadronic branching ratio of $W^{\pm}$ decays and by tagging the flavour of hadronic jets produced in $W^{\pm}$ decays. Applying the two methods to the data collected during 1996 at energies of 161 and 172 GeV, DELPHI obtains $|V_{cs}| = 0.91{+0.15 \atop -0.14}({\rm stat})\pm 0.05({\rm syst})$.