Final force balance for the early O-star model in Table 1. Lower panels of both figures: the solid lines and black squares show Γ = g_rad ∕g on the discrete mesh points and the red dashed line values for the rest of the terms in the e.o.m., Eq. (2), i.e., (1 − 2a²∕r + da²∕dr + vdv∕dr(1 − a²∕v²))∕g. Since the e.o.m. is perfectly fulfilled, the solid black and dashed red lines lie directly on top of each other in the figure. The dotted lines mark the sonic point v = a. Upper panels: absolute value of the error f_err (Eq. (13)) in the e.o.m. The abscissae in the upper figure show velocity v and in the lower scaled radius r∕r_c − 1, with r_c the lower boundary radius of the simulation.