The minima times of GW Car, V742 Cen and V764 Sco were determined from
our observations (van Houten et al. 2003) using Kwee & van Woerden’s (1956)
method for each Walraven passband separately. These data were used to find
the mean value of the minimum including its standard error σ. The weight of
the minimum was calculated by a usual way as 1/σ 2 . Due to the bad coverege
of minima by observations for V685 Cen, we used them only to find the normal
epoch of the primary minimum