Analysis system for the photometric determination of an analyte in a body fluid, the analysis system comprising an analysis instrument and a test carrier, the test carrier comprising an evaluation zone in which a photometrically detectable change occurs as a result of a reaction of a sample of the body fluid contacted to the test carrier with a reagent contained in the test carrier, the analysis instrument comprising: an optical emitter for emitting light onto the evaluation zone of the test carrier; an optical receiver for receiving light from the evaluation zone and for generating a measurement signal corresponding to the received light; a measuring and evaluation device having a measuring unit and an evaluation unit, wherein the measuring unit is capable and adapted for amplifying and digitizing the measurement signal generated by the receiver, the evaluation unit is capable and adapted for determining a desired concentration value from the digitized measurement signal using an evaluation algorithm, which comprises an assignment of concentration values to the values of the digitized measurement signal, the assignment being production-method-specific and dependent on the test carrier used, wherein in the evaluation algorithm at least one computing step is executed by means of a processor, the evaluation unit is capable and adapted for acquiring in the algorithmic sequence of steps the concentration value at an acquisition point downstream from the execution of the computing step, the concentration value is verified by means of a control algorithm by determining a deviation of the determined concentration value from a reference concentration value, characterized in that a reference assignment in the control algorithm is used, the reference assignment assigning a plurality of reference concentration values to a plurality of reference measurement values, and wherein, using the reference assignment, the reference concentration value is determined from a reference measurement value which is adjacent to the current measurement value of the measurement signal or which is a specific number of reference measurement values away from the current measurement value of the measurement signal, and the analysis system is capable and adapted for recognizing an error of the measuring and evaluation device if the deviation of the concentration value from the reference concentration value exceeds a predefined limiting value. an optical emitter for emitting light onto the evaluation zone of the test carrier; an optical receiver for receiving light from the evaluation zone and for generating a measurement signal corresponding to the received light; a measuring and evaluation device having a measuring unit and an evaluation unit, wherein the measuring unit is capable and adapted for amplifying and digitizing the measurement signal generated by the receiver, the evaluation unit is capable and adapted for determining a desired concentration value from the digitized measurement signal using an evaluation algorithm, which comprises an assignment of concentration values to the values of the digitized measurement signal, the assignment being production-method-specific and dependent on the test carrier used, wherein in the evaluation algorithm at least one computing step is executed by means of a processor, the evaluation unit is capable and adapted for acquiring in the algorithmic sequence of steps the concentration value at an acquisition point downstream from the execution of the computing step, the concentration value is verified by means of a control algorithm by determining a deviation of the determined concentration value from a reference concentration value, characterized in that a reference assignment in the control algorithm is used, the reference assignment assigning a plurality of reference concentration values to a plurality of reference measurement values, and wherein, using the reference assignment, the reference concentration value is determined from a reference measurement value which is adjacent to the current measurement value of the measurement signal or which is a specific number of reference measurement values away from the current measurement value of the measurement signal, and the analysis system is capable and adapted for recognizing an error of the measuring and evaluation device if the deviation of the concentration value from the reference concentration value exceeds a predefined limiting value.