Technique for measuring photometric accuracy

A convenient photometric linearity test that meets stringent criteria for accuracy and practicality is described. Experience with alternate, commonly advocated methods illustrates the need for an improved approach. The method described herein relies on direct application of physical principles. It combines use of Bouguer's law and superposition of optical fields. Each technique overcomes a deficiency in the other. Peak errors in absorbance were found to be 0.0011 or less in a commercial spectrophotometer equipped with a specially calibrated potentiometer and were primarily attributable to phototubes.