Best orbital fits and residuals. Upper panel: O – C diagram of QS Vir. The crosses and plus symbols represent the O – C values built with the linear and quadratic ephemeris, respectively (O – C = T_calc-Eq. (2)). The solid line and the dashed line represent the models fitted using the two models as described in the text. Lower panel: residuals using the same symbol and color coding as the top panel.