Long-term variations of the rotation period and O-C values for the magnetic chemically peculiar star CU Vir. Left: the model curve of long-term rotational period changes ΔP of CU Vir in seconds with respect to the mean period P₀ = 0ḍ52069415. The formal accuracy of the polynomial fit is comparable with the thickness of the fitted line. Right: the difference of the observed and calculated times of zero phase according to a linear ephemeris in days. Each point represents the average of 498 consecutive individual measurements; the weights of these means are indicated by their areas.