1-σ uncertainty ellipse for the optimum initial rotational period and YORP strength of the spin-state model to produce the best fit between artificial lightcurves and observations. YORP-spin up is required, with the best-fit obtained using 12.1323789 h for the sidereal rotation period at T₀ and a corresponding YORP strength of 3.81 × 10^-8 rad day^-2. From the 1-σ uncertainty ellipse we determine the uncertainty in period to be 4.7 × 10^-6 h and the corresponding uncertainty in YORP to be 0.24 × 10^-8 rad day^-2. Note that in this case where we have a spacecraft shape model with a well-determined pole solution, the uncertainty in the fitted initial period becomes the dominating influence on the uncertainty in the measured YORP value.