VDA schematics. The schematic is colored as follows. (black) Control regions; (white) sites where high reliability ABACUS calls could be made; (red) sites with signal saturation; (violet) sites with low signal; (green) sites where different models fit best on the forward and reverse strand; (blue) sites where no model reached the total threshold; and (yellow) all other sources of failure. Both of these schematics come from VDA design CWRS-13. (a) An excellent VDA—very little failure of any kind distributed relatively evenly across the VDA. (b) PCR failure—the last PCR primer pair failed. Notice small spots of white mixed among the failure.