First-harmonic phase of time-resolved pulse profiles extracted along the Cen X-3 observation on 2015 November 30 with time tagged since its start. Pulses are extracted every 1500 s and rebinned to achieve a S/N of 15. The solid line with spread indicates the best linear trend and its 1σ envelope. The phases are obtained by folding the light curve using the period and period derivative shown in Table 1.