Time axis for each individual. The initial time of the integration and the first computedtransits are marked with vertical lines (lower labels); the observed transits are marked with dots (upper labels). At the first computed transit, a Julian date is assigned to t_1,com corresponding to t_1,obs. In this way, the instant t_init defining the elements gets a BJD_TDB equal to the first transit minus the time elapsed since the start of the integration.