All Oakton Traceable conductivity standards are NIST-traceable reference materials Supplied with a calibration report from an ISO 17034 and ISO 17025 accredited laboratory These standard solutions let you calibrate conductivity instruments to ensure accuracy If unopened, shelf life is one year; once opened, shelf life will vary by solution value. Oakton Traceable One-Shot™ conductivity and TDS standards include detailed KCl, NaCl, and 442 conversions, temperature corrections, and certified values referenced to 25Cconvenient!! Average accuracy at 25C is 0.25 microsiemens for 1, 5, 10 microsiemen (S) solutions, or 0.25% for all other solutions.