Top: a close-up of the Fourier transform of the light curve of KIC 6678174 (black) and the accepted frequencies in the region where the detected period spacing series is located. The frequencies which were accepted for α = 0.5 are marked with full grey lines, and the ones for which α< 0.5 are marked with dotted lines. Bottom: the period spacing as computed for the (accepted) frequencies shown in the top. The white markers indicate the spacings for frequencies accepted for α< 0.5, while the dotted lines indicate the regions where there are likely frequencies missing.