A device for determining the result of an assay may include a computation circuit, responsive to a signal representing the amount of an analyte or the rate of accumulation of an analyte, to: compare the signal to a first threshold; compare the signal to a second threshold, the second threshold being less than the first threshold; generate an output signal if the signal exceeds the first threshold or the signal is less than the second threshold, the output signal indicative of a first result if the signal exceeds the first threshold, or, alternatively, the output signal indicative of a second result if the signal is less than the second threshold; and terminate the assay if the signal exceeds the first threshold or the signal is less than the second threshold.