Spectral index uncertainty maps of Abell 2256, including a systematic 10% flux scale uncertainty and map noise, at different frequencies with the restoring beam shown in the bottom left inset. Both maps have been smoothed to a common resolution of 39″ × 24″. The median uncertainties are 0.31 and 0.19 in the left and right image, respectively. The contours show higher frequency [3, 6, 12, 24, 48]σ levels where σ denotes the background rms noise level.