IOTA is a very simple high-speed scanning spectrophotometer. A computer, an essential part of the tool, controls data acquisition, corrects systematic errors, normalizes data, and provides data reduction for the specific problem of measuring the thickness of thin oxide films on silicon semiconductor wafers. Data reduction techniques used with this computer-controlled measurement are different from those conventionally used with manually acquired data. Independence from operator induced bias and error is obtained with fully automatic measurement. © 1972.