Bio-Rad Model 680 Microplate Reader Accessories - Manual (Page 18)

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The result absorbance value of the formula calculation and the gray zone value
that is entered by the user are used for the cutoff. The upper and lower cutoff
values are:
Upper cutoff absorbance = Result of a Formula + ((Gray zone/100) * Result of a Formula)
Lower cutoff absorbance = Result of a Formula - ((Gray zone/100) * Result of a Formula)
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 (-).
d. Cutoff Ratio
The mean absorbance value of the Calibrator wells defined in the plate map and
the concentration value entered by the user are used for the cutoff ratio. Before
the cutoff, the absorbance value of each well is converted into the concentration
value. The ratio of Concentration/Absorbance of Calibrator is applied to the
conversion. Then, the cutoff is done with the defined Positive and Negative or
the defined Positive and Gray zone values.
Ranged Cutoff Control
The concentration range of the Positive and Negative is divided into 10 equal
partitions, numbered 0 through 9. The concentration 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 concentration greater than the Positive are
reported by plus signs (+), and wells with concentration less than the Negative
by minus signs (-).
Single Cutoff Control
The concentration value of the Negative and the gray zone value entered by the
user are used for the cutoff. The upper and lower cutoff values are:
Upper cutoff concentration = Positive + ((Gray zone/100) * Positive)
Lower cutoff concentration = Positive - ((Gray zone/100) * Positive)
The concentration range of the upper and lower cutoff is divided into 10 equal
partitions, numbered 0 through 9. The concentration 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 concentrations greater than the upper
cutoff are reported by plus signs (+), and wells with concentrations less than the
lower cutoff by minus signs (-).
(6) Curve fit report
The Curve fit report provides a regression analysis based on the absorbance values
of a series of standards. There are ten types of curve fits supported with the
onboard software on Model 680 microplate readers: