A thermometric device unequivocably showed whether samples complied with a standard, to a resolution better than 0.002 aw units, without calibration, and with a throughput of one sample per 6 min. As a meter its response was linear from aw = 0.78 (the lowest value tested) to 1.00. It exhibited no hysteresis and was immune to drift resulting from high humidities or contamination by nonaqueous volatiles from foods.