A representative sample of lightcurves generated using the convex model of Itokawa. The solid line represents the artificial lightcurves and the dots are the observed magnitude data points. In the upper panels, the model has been advanced with a rotation period changing due to YORP. In the the lower panels, the lightcurves are generated with a fixed period model. It is clear that there is a progressive increase in the rotation phase offset between the artificial lightcurves and observed data points when a fixed period model is used. Incorporating a linear change in rotation rate, consistent with YORP, corrects the rotational phase of the artificial lightcurves (also see Fig. 1).