Top: matter power spectrum (including non-linear corrections using the fitting form of Takahashi et al. 2012) at redshifts 0 and 2, predicted by the ΛCDM model with a single massive neutrino of 0.06 eV (dashed curve) or allowing the neutrino mass to float (dotted curve). Bottom: fractional error in each power spectrum, compared to the average plotted above, due to the remaining uncertainties in the cosmological parameters. Uncertainty in the evolution of the scale factor at late times (due to dark energy) leads to an additional uncertainty in the overall amplitude, coherent across scales, which is not shown here. With current BAO and SNe data the uncertainty in the growth from z  =  2 to z  =  0 is 8% (or 16% in power).