Implementations disclosed herein provide a method of determining a quantity of an electrochemically convertible substance in a fluid sample, the method comprising introducing the fluid sample into an electrochemical sensor, wherein at least a portion of the fluid sample is electrochemically converted to produce an electrical output from the electrochemical sensor, measuring the electrical output from the electrochemical sensor on a periodic basis to produce sensor measurements, inputting a first subset of the sensor measurements into a first computation to yield first computation analysis results, inputting a second subset of the sensor measurements and the first computation analysis results into a second computation to yield second computation analysis results, and calculating the quantity of the electrochemically convertible substance in the fluid sample by applying a third computation to the first computation analysis results and the second computation analysis results.
