  We demonstrate a method for accurately locking the frequency of a
continuous-wave laser to an optical frequency comb in conditions where the
signal-to-noise ratio is low, too low to accommodate other methods. Our method
is typically orders of magnitude more accurate than conventional wavemeters and
can considerably extend the usable wavelength range of a given optical
frequency comb. We illustrate our method by applying it to the frequency
control of a dipole lattice trap for an optical lattice clock, a representative
case where our method provides significantly better accuracy than other
methods.
