This Document includes, in addition to the introductory Chapter 1, the following three parts: — Chapter 2 which concerns the theoretical structure of a hierarchy scheme; it describes the different levels, corresponding standards, and the passage from one level to another; it also includes certain considerations relating to an international hierarchy scheme, — Chapter 3 which, completed by Appendix I, gives the information which should be included in a hierarchy scheme and in the description of a calibration chain, enabling States to set up national calibration chains, in their own countries, according to their needs and according to their facilities, — Appendix II which gives an example of a calibration chain, for measuring instruments for a given quantity; the calibration chain is a practical realization of the corresponding hierarchy scheme; the comments included in this part explain the different possibilities of a calibration chain structure. The purpose of this Document is: — to propose general rules for the establishment of hierarchy schemes for measuring instruments for different quantities. These schemes lead to practical realizations, described in the text as calibration chains, — to define and explain the concepts used in these schemes.