Mass standards are reference materials used to ensure accurate measurements of mass in scientific and industrial applications. These standards are typically made from materials with known densities and are calibrated to precise values, allowing for consistency in weighing processes. In many countries, mass standards are maintained by national metrology institutes, such as the National Institute of Standards and Technology (NIST) in the United States. These institutions provide calibration services and ensure that mass measurements align with international standards, promoting accuracy and reliability in various fields, including manufacturing and research.