A method to track stability and performance of diagnostic instrumentation, especially for veterinary automated hematology analyzers, applies a weighted moving averages algorithm to the diagnostic results of patient samples calculated by the analyzer. Control chart rules are used to set limits or ranges in order to determine if weighted averaged diagnostic results are within or outside of such limits or ranges. If the weighted average diagnostic results are outside of such control chart rule limits, then fuzzy logic and a gradient descent algorithm are applied to the weighted averaged diagnostic results.