Write down the formula as follows:
y = d + (a -- d)/ [1 + (x/c)b]
Find the value of a. This is the response value at zero concentration, or the minimum asymptote.
Find the value of b. This is the steepness of the curve, or Hill Slope, or slope factor. The steepness value can either be positive or negative.
Find the value of c. This is the point in the curve where the curvature of concavity changes directions, also known as the mid-range point.
Find the value of d. the response value for infinite concentration, or the maximum asymptote.
Determine x. This is the dilution. To find a base relative solution to run, follow the formula:
Relative dilution = (actual sample / max dilution in series) * 100
Calculate for y. Once all the values are known, y can be calculated. These numbers are very accurate when determining the optical density for the sigmoidal shape.