Abstract: In an automatic chemical testing apparatus in which radiant energy readings are taken from a liquid sample of reacted contents comprising reagent and one or more aliquots, one per channel, of a sample fluid, a statistically large number of readings are taken on each sample. For example, in a readout cycle, 32 readings are taken on each channel for a sample. For an end point chemistry, calculation of an output value is based on the mean of a plurality of readings which are a subset of all readings. For a kinetic chemistry, the output reading is based on a slope of a curve defined by subsets of successive readings.

Abstract: In an automatic chemical testing apparatus calibration values obtained from readout signals of analysis means must be stored for use in prior art calculating means for processing of subsequent readout signals of samples containing unknown quantities of substances in a medium. Improved means are provided for selecting the calibration values, namely a blank value and a reference value. A plurality of pairs of blank and reference samples are processed. The blank samples have known zero or baseline levels or concentrations of substances, and the reference samples have known concentration levels of each substance. These known values are stored for comparison to processed values obtained by processing the readout signals obtained in response to analysis of the blank and reference samples. The validity of each such readout signal as a calibration value is determined by the successfulness of the comparison. The most current successful blank and reference signals are selected as the calibration values.