Use Standards with all meters Traceable® Conductivity Standards, a Certified Reference Material, are 100% compatible with all makes of instruments and probes. Traceable® Conductivity Standards are the most accurate available. Accuracy at 25°C is (±0.25 microsiemens for 1, 5, 10 microsiemen solution or ±0.25% for other solutions) or the uncertainty shown on the certificate, whichever is greater. Each bottle is labeled for calibrating conductivity (microsiemens/micromhos), resistivity (ohms), and dissolved solids (parts per million). Methods supported This certified reference material meets test requirements for Federal, State, and local agencies, CAP, ASTM, NCCLS, CLSI, ACS, CLIA, AOAC, EPA, APHA, AWWA, WEF, USGS, USP, and ISO. Traceable® Certified Reference Material complies with and is essential for use in these official methods: AOAC 973.40, EPA 120.1, Standard Method 2510 (APHA, AWWA, WEF), ISO 7888, DIN 38404, ASTM D1125, USGS I-1780, USP 645, and for A2LA/NVLAP accreditations/ISO 9000 certifications. Material may be used to calibrate all conductivity meters and to determine all conductivity cell constants.