APT optical photometry of 55 Cnc. First and second panels: seasonal mean differential magnitudes of 55 Cnc (P) with respect to comparison stars C2 and C3. Third panel: seasonal mean differential magnitudes between comparison stars C3 and C2. The dotted lines show the grand means for all three panels. The total range of the observations and the standard deviation of the seasonal means from the grand mean are shown in the lower left and lower right of each panel, respectively. The C3 − C2 differential magnitudes show excellent stability of ± 0.00025 mag, demonstrating that the variability in the P −C2 and P − C3 light curves is intrinsic to 55 Cnc.