  We discuss precision measurements of the leading atmospheric parameters at a
standard neutrino factory. The oscillation of the muon and electron neutrinos
(anti-neutrinos) to tau neutrinos (anti-neutrinos) adds to the muon events
sample (both right sign and wrong sign) via leptonic decays of the taus
produced through charge-current interactions in the detector. We focus on how
this contribution affects a precision measurement of the atmospheric mixing
parameters and the deviation of muon neutrino -- tau neutrino mixing from
maximality.
