The NSF/ANSI 50 certification mark on a water quality testing device (WQTD) used in recreational waters, such as pools and spas, means that the product was reviewed and certified by NSF International to meet applicable American National Standards for product design and performance. NSF tests and re-tests products to confirm that they comply with all requirements of certification for performance, accuracy and operating range. The WaterLink SpinTouch gained the highest accuracy rating of L1 for its tests for pH, free chlorine, combined chlorine and cyanuric acid.