Upper panel: pulsation period lengths over time using LC data (black) and SC data (gray). Note the fluctuations of variance. The peaks are indicated with triangles at P₁ = 0.24 days. In addition, there are "forbidden zones," e.g., at BJD = 1500: P₁ = 0.265d. This diagram can easily be understood as the typical O−C (observed minus calculated) diagram if the average main pulsation period P₁ = 0.269 is set to zero. Periods longer than P₁ then have positive O−C values and vice versa. Lower panel: zoom showing the progression of subsequent period lengths.