For liquids heavier than water, each hydrometer is calibrated in a triple accredited ISO/IEC 17025:2005, A2LA accredited laboratory against equipment whose calibration is traceable to NIST. Individually packaged with a multi-language Statement of Accuracy indicating accuracy traceable to NIST. NIST Traceable. Temperature of Standardization 60°F/60°F. Metal Ballast. Individually Serialized 5 year warranty