Fixed-point iteration applied to the batsch1 data set. The estimated amplification efficiency, (E - out, vertical axis), varies according to the assumed amplification efficiency (A - In, horizontal axis) used to construct the sigmoid reference curve. The red line is a plot of (E - out) as a function of (A - In). Applied iteratively, however, the process converges to the point of intersection of the red curve and the line of identity (black). This point of convergence, the fixed-point, is independent of the starting value. With a starting value of A=1.5 the first iteration is shown in blue, the second in green.