Definition - What does Primary Standard mean?
A Primary Standard is a set of standard parameters that are used in metrology and in other interest areas of studies as reference to determine certain factors. The standards are considered to be accurate, cannot be calibrated by, and become a reference to other measurement standards. The primary standards are recognized globally in all industries and consist of accreditations by globally recognized standard authorization bodies. An example of a primary standard is the international prototype kilogram which is the mass standard for the International System of Units.
Petropedia explains Primary Standard
A primary standard is defined via other quantities like length, mass and time. The primary standards are the reference or subordinate to the secondary standards which means that in order to get a pass certificate from an issuing authority an object has to meet all the requirements mentioned as per the primary standards.
The secondary standards are called working standards, which are basically derived from primary standards. The primary standards are never used directly for performing any measurements rather they are used mainly for comparing the results obtained from secondary standards or working standards.