Abstract: In a scanning spectrophotometer, in which a narrow wavelength band of radiation can be selected from a range of wavelengths for transmission alternately through a sample cell and a reference cell, continuous automatic baseline correction is provided. A pulse train signal is generated, wherein the number of pulses represents the ratio of a parameter (e.g., intensity) of the radiation transmitted, respectively, through the sample and reference cells. A ratio of unity represents the baseline, and deviations from the baseline are indicated by changes in the number of pulses in the pulse train. Digital information indicative of baseline deviations is stored in a memory device when the spectrophotometer is being calibrated, and is retrieved from the memory device during operation of the instrument for sample analysis. The retrieved information generates a correction signal, which provides a continuous baseline correction.