For over 20 years National Standards of Puerto Rico has set the standard for precision committing to achieving the highest measurement capability and offering the lowest measurement uncertainties possible. Our MASS LABORATORY is equipped with fully automatic comparators. These automatic comparators perform multiple unattended repetitive measurements that are analyzed. This results in small deviations and a very high level of confidence in the measured values. Each comparator is assigned to a specific range of weight, from 1kg to 100g, from 100g to 10g, and from 0,5mg to 5 g. The excellent environmental control and standard calibration procedures provide them the best conditions to work within their stated capabilities. Specially designed for NSPR, the marble tables complete the platform of our METROLOGY LABORATORY. Due to these superior environmental controls, standard procedures and advanced technologies, NSPR provides highly reliable calibration instrument service and solutions. Traceability to NIST and PTB are maintained through three (3) E0 Super Primary Standards (SPTS) 1kg, which are certified by these agencies. Our Primary Reference Standards (PRS) are verified periodically with reference to the SPTS. This PRS are used to calibrate our working standards and to verify measuring capabilities. Thus our calibration services assure of the highest standards of measurement quality. Accredited by the National Voluntary Laboratory Accreditation Program for the specific scope of accreditation under lab code 200454-0, our Mass Laboratory is equipped with the most advanced comparators available in the market capable of calibrations with accuracies to 0.1 ?g and state of the art environmental controls. On-going mass inter-laboratory comparison provides periodic checks on our measurement methodologies.