Traceability is the property of the result of a measure whereby this result can be related to or refer to the standards or references of the highest level and through them to the fundamental units of the International System (SI) by means of an uninterrupted chain of Comparisons.
When the chain is traversed in the opposite direction, that is, from top to bottom, there is talk of dissemination of the unit. Thus there is a pyramidal structure in which at the base are the instruments used in the current measurement operations of a laboratory. Each step or intermediate step of the pyramid is obtained from the one preceding it and gives rise to the next step by means of a calibration operation. At each step are instruments and patterns that in turn act as patterns or references of the following.
As each comparison of the chain introduces new causes of error that give rise to new contributions to the uncertainty of the result, which add to the uncertainty with which the value of the starting pattern is known, it is necessary that the uncertainty of the primary patterns is very lower than those required in ordinary applications. This pyramidal grouping is what is called a calibration and validation plan, which will ensure that all equipment and standards have the appropriate traceability to national or international standards.