Observed and interpolated V-band light curve of NGC 4151. The blue filled circles are the observed V data points. Error bars are plotted but smaller than the symbols in most cases. Based on these observations, 50 interpolated light curves have been calculated and are shown as gray dotted lines, reflecting the uncertainty of the “true” light curve. The red dashed line indicates the mean of all these models, which has been used as the input signal to our model simulations.