This document is a user manual that provides instructions on how to use the 47001-88 2100AN Desktop Turbidity Meter and explains its operating principles. It also provides detailed instructions on how to measure turbidity, including preparation steps and testing techniques. The manual covers the use of the instrument's control panel and indicator lights, as well as calibration and special research applications. Additionally, it includes information on the gas purification system, the use of the flow cell system, data output, and setting the instrument's clock.