  We describe our algorithm for measuring the Hubble constant from Ryle
Telescope (RT) interferometric observations of the Sunyaev-Zel'dovich (SZ)
effect from a galaxy cluster and observation of the cluster X-ray emission. We
analyse the error budget in this method: as well as radio and X-ray random
errors, we consider the effects of clumping and temperature differences in the
cluster gas, of the kinetic SZ effect, of bremsstrahlung emission at radio
wavelengths, of the gravitational lensing of background radio sources and of
primary calibration error. Using RT, ASCA and ROSAT observations of the cluster
Abell 1413, we find that random errors dominate over systematic ones, and
estimate H_0 = 57^{+23}_{-16} km/s/Mpc (1-sigma errors).
