Top: two examples from a time series of 28 artificial surface temperature maps as snapshots of a differentially rotating test star applying α = 0.006 surface shear. Below, in the second, third, and forth rows plotted are the corresponding recoveries assuming no data noise, S/N = 200, and S/N = 100, respectively. Phases of the artificial observations are indicated by arrows underneath. In the righthand column, the retrieved DR functions are plotted as best fits (continuous lines) for the correlation patterns of the average cross-correlation function maps. The respective shear parameters are α = 0.0058 ± 0.0002 (no noise, right top), α = 0.0067 ± 0.0006 (S/N = 200, right middle), α = 0.0069 ± 0.0012 (S/N = 100, right bottom).