ProCal Primary Turbidity Standards have been certified by HF Scientific for use in the Hach® 2100N Laboratory Turbidimeter. No formazin is used, making the standards safer, easier to use, accurate and less expensive that the equivalent Hach® product. In addition to being approved by the EPA, ProCal™ has been certified through testing conducted by HF Scientific demonstrating that ProCal™ performs as well as Hach® primary turbidity standards in selected Hach® instruments. Test results are available upon request. Hach® is a registered trademark of the Hach Company, which is not affilitated with HF Scientific.