Speedup factor of Optimal BLS relative to the unoptimized BLS vs. the span of the simulated dataset (10, 20, 40, 80, 160 and 320 days). The different lines are the ratio of run times measured for different runs, each one for a different group size (1, 10 and 100 stars per group, in blue circles, green squares and red triangles respectively). The solid black line is the predicted speedup factor from Eq. (16) and is not a fit. See text for further discussion.