Bio-Rad Model 680 Microplate Reader Accessories - Manual (Page 17)

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Upper cutoff absorbance = Positive absorbance + ((Gray zone/100) * Positive absorbance)
Lower cutoff absorbance = Positive absorbance – ((Gray zone/100) * Positive absorbance)
For units not designated "Abs", the absorbance value of each well is converted
to the concentration value using the curve fit constants of the curve fit report. If
the concentration of a well is within the gray zone value of the positive cutoff
value, the well is scored "*". If the concentration of a well is more than the gray
zone value greater than the positive value, the well is scored "+", and if the
concentration of a well is more than the gray zone value below the positive
value, the well is scored "-".
Upper cutoff conc. = Conc. of positive controls + ((Gray zone/100) * Conc. of positive controls)
Lower cutoff conc. = Conc. of positive controls - ((Gray zone/100) * Conc. of positive controls)
b. Cutoff Control
Ranged Cutoff Control
The mean absorbance values of the Positive and Negative wells defined in the
plate map are used for the cutoff.
The absorbance range of the Positive and Negative is divided into 10 equal
partitions, numbered 0 through 9. The absorbance value of each well is
classified according to the partition of the matrix to which it corresponds, and is
reported as a signal digit. Wells with absorbance values greater than the
Positive are reported by plus signs (+), and wells with absorbance values less
than the Negative by minus signs (-).
Single Cutoff Control
The mean absorbance value of the Negative wells that defined in the plate map
and the gray zone value that is entered by the user are used to the cutoff. The
upper and lower cutoff values are:
Upper cutoff absorbance = Mean of negative controls + ((Gray zone/100) * Mean of negative controls)
Lower cutoff absorbance = Mean of negative controls – ((Gray zone/100) * Mean of negative controls)
The absorbance range of the upper and lower cutoff is divided into 10 equal
partitions, numbered 0 through 9. The absorbance value of each well is
classified according to the partition of the matrix to which it corresponds, and is
reported as a signal digit. Wells with absorbance values greater than the upper
cutoff are reported by plus signs (+), and wells with absorbance values less than
the lower cutoff by minus signs (-).
c. Cutoff Formula
The mean absorbance values of the Positive and Negative wells defined in the
plate map are used for the cutoff formula calculation.
The 12 types of formula supported are:
i. k * CNx vii. k + CNx
ii. k * CPx viii. k + CPx
iii. k * COx ix. k + COx
iv. CNx / k x. k*CNx + CPx
v. CPx / k xi. (CNx + CPx) / k
vi. COx / k xii. k1*CNx + k2*CPx