Automatic calculation of the FCD error cutoff. (a) S. aureus de novo assembly (k-mer of 71). (b) P. falciparum de novo assembly (k-mer of 55). In each plot, the black line shows the proportion of windows that would be called as an error for a range of cutoff values. The green and blue lines are the first and second derivatives of the black line, normalised to lie between -1 and 1. The vertical red line marks the FCD error cutoff, automatically determined by REAPR as the first FCD score corresponding to first and second derivatives ≥0.05.