The HM Digital SM-1 Single Inline TDS Meter is designed for measuring the Total Dissolved Solids (TDS) in a single water line, making it an excellent tool for monitoring your reverse osmosis system. Typical monitoring points include the pre-system, post-membrane, or post-deionization stages. This unit is equipped with a digital display and includes a 1/4" GA Murdock Quick Connect Tee with dual o-rings for a secure seal. Like all HM Digital products, the SM-1 is factory calibrated.