Example observations of V1636 Ori from March 20, 21, and 22, 2009 at the CAHA (left, from top to bottom), combined used as one O–C measurement. The error bar on the left of each plot represents the photometric uncertainty. The red line shows the simultaneous two frequency fit to the epoch data. The amplitude spectra on the right hand side show the spectrum of the full data set (top), the spectrum of this epoch (middle) and the respective window function computed at f₁.