Example of GP fit to a r-band light curve (top). The GP fit is shown as a red and the 1σ uncertainty is shown as the red shaded region. The area over which the integrated flux under the secondary maximum, ℱ_r2, is calculated is indicated by the grey shaded region, and t₂(r) by the black dashed. The first derivative of the GP light curve (middle). This light curve has a secondary shoulder rather than a secondary maximum because the first derivative is not equal to zero. The second derivative of the GP light curve (bottom), shows that the time of the onset of the secondary maximum is the time at which the second derivative is equal to zero, also known as an inflection point.