Average cross-correlation function map of σ Gem from the NSO 1996−97 data set. The resulting differential rotation pattern for the combined (Fe+Ca) time-series Doppler images gives evidence of antisolar-type differential rotation. The background shade scales the strength of the correlation (white: no correlation, dark: strong correlation). The dots are the correlation peaks per 5°-latitude bin. Their error bars are defined as the FWHMs of the corresponding Gaussians. Assuming a quadratic DR law, the derived surface shear parameter α is − 0.04 ± 0.01.