The company acquired APS Analytical Standards, a maker of turbidimeters, colorimeters, and spectrometers. There are various calibration methods for tristimulus colorimeters. Early products included microscopes, burets, pipettes, litmus, balances, colorimeters, dissecting kits, and anatomical models. Instruments used for measuring device colors include colorimeters and spectrophotometers. In digital imaging, colorimeters are tristimulus devices used for color calibration. On the other hand, tristimulus colorimeters are purpose-built, cheaper, and easier to use.