Apparatus and method for sensing and measuring optically active material in a sample, comprising: a) a light source emitting light of a wavelength that can pass through the sample; b) a light transparent sample container for holding the sample; c) a linear polarizer interposed between the light source and the sample for producing a polarized light beam; d) a symmetrical linear split-field polarizer fixedly positioned to intercept the polarized light that passed through the sample; e) detectors to detect the split light beams passing through each polarizer of the split-field polarizer; f) means to amplify the current or voltage passing through each of the detectors; g) a differential amplifier; h) a data processor; i) a display; and j) electronic circuitry to operate the apparatus and provide an output on the display.