Reference reading in an analyzer

Claim 1

In a method for quantitatively assaying for an analyte in a biological liquid, comprising the steps of a) scanning with a light beam a test element bearing a sample of liquid having an analyte of unknown concentration; b) scanning a reference element with said light beam; c) detecting the amount of light diffusely reflected from said test element and said reference element; d) filtering the light beam before or after reflection from said elements and before detection, at a preselected wavelength that is the same for both said test element and said reference element; e) storing the detected amounts of diffuse reflection for each scanning of the reference element and test element, and f) comparing the detected reflectance of the test element with said stored reference detected reflectance to determine how much analyte is present, said reference element being scanned repeatedly, each time for a predetermined multiple of test elements scanned, a reference reflectance value being stored for each scanning; the improvement wherein said step e) comprises the steps of always selecting from said stored reference reflectance detections at said wavelength that which is either detected by step c) at a point of time closest to the time at which said test element is scanned at said wavelength in step a), or that which is computed to be the equivalent reference reflectance at the actual time the test element reflectance was read, and comparing said selected reference reflectance detection in said step f) with the detected test element reflectance, whereby the effect of drift in the reading of the reference element is minimized.