These hydrometers are manufactured, inspected, and tested to exacting standards. The accuracy, uniformity, and dependability of each Hydrometer is assured due to individual testing procedures. The calibration standards of each hydrometer are directly traceable to the National Institute of Standards and Technology (NIST) and DKD. The hydrometer we offer comes with a calibration report that includes a list of actual corrections to 1/10 of a division, accuracy for temperature or density correlated to NIST standards and a statement of traceability to NIST standards.