The Safe Dip tester is a hand-held, digital meter, designed to make measuring several important pool and spa chemistry test factors. It can test for Salt, TDS (Total Dissolved Solids), Free Chlorine, pH, ORP (Oxidation-Reduction Potential) and Temperature. The ability to test for salt makes this an especially ideal tester, for use with salt chlorine generators. The TDS test helps manage extreme hard water problems. The Safe Dip Tester is all-digital and is easy to use. Simply fill the built-in sampling cup, with pool or spa water, and press the Start button to get a test reading..