, Traceable conductivity standards are Certified Reference Materials, making one of the most accurate availableAll Oakton Traceable conductivity standards are NIST-traceable reference materialsSupplied with a calibration report from an ISO 17034 and ISO 17025 accredited laboratoryThese standard solutions let you calibrate conductivity instruments to ensure accuracyIf unopened, shelf life is one year; once opened, shelf life will vary by solution valueOakton Traceable Conductivity and TDS Standard, Batch-Tested, 200,000 µS; 500 mL