Many people still struggle with the concept ‘metrological traceability’ and have trouble when attempting to define it. Yet, it is basically simple: metrological ‘‘trace’’ability is about our ability to demonstrate the ‘‘trace’’ along which we can show how our measurement result is connected to a commonly agreed reference. Since a measurement is always a comparison, we need a reference against which we can perform such a comparison. That reference can be: (a value of) a measurement unit, a measured value of a measurement standard (calibrator, mostly called a CRM), or a measured value obtained by a commonly agreed reference measurement procedure, along a ‘‘track’’ or ‘‘pathway’’ consisting of a transparent, unbroken chain of links. Hereby, ‘calibrator’ is meant to be a material, not a person. As for all ‘concepts’ we use in our thinking, it is essential for our mutual understanding that we have the same concept in mind for the same thing we are reflecting on. So it is for the concept ‘metrological traceability’ [1] of a measurement result. Let us see how said ‘‘trace’’ is manufactured almost automatically when we start measuring, and identify the very operation which manufactures the first link of the ‘‘trace’’. We do that by means of a simple example: measuring ‘mass’ (one member of the big family of things we intend to measure, i.e. ‘measurands’) of, e.g. meat (note: we use single quotation marks to designate a concept). The purpose of measuring is to assign a numerical value to that measurand, i.e. to the ‘mass’ of the meat. We do that by comparing the mass of the meat to a known value of the same measurand (i.e. mass) carried by—or embodied in—a piece of metal with a known mass, called a ‘‘weight’’. Such a known value in a carrier (which can be, among others, a simple material or a complex ‘‘matrix’’ material) is our ‘reference’. So, in this example, the operation of measurement consists of assigning a value to a measurand, (the mass of the meat) derived from a comparison to a known value of the same quantity, embodied in a ‘reference’ (carrier here called a ‘‘weight’’). To perform that measurement, we build or purchase a measuring system—in the above example, a balance— which enables us to carry out the comparison to the ‘reference’. Usually such a reference is called a Certified Reference Material [2], but the (better) generic name is ‘measurement standard’ [3] or ‘calibrator’ [4]. The whole process is called a calibration and the ‘measurement standard’ or ‘CRM’ acts as a ‘calibrator’ [4] of our measuring system (the balance). We can then use this ‘‘calibrated’’ measuring system (the balance) to assign a value to the measurand (the mass of meat) which is embodied in the material sample (the meat) under investigation. Measurement finished. End of story. Note: it is useful to consider that ‘measurement standard’ is a more generic concept, i.e. the name of a family of concepts of which ‘calibrators’ and ‘CRMs’ are members. Without thinking about it, we have in fact established the first link of the metrological traceability chain of our measurement result. This first link consists of the bridge built by comparing the value embodied in our sample and previously unknown, to the known value embodied in a measurement standard. The traceability chain of the quantity value embodied in such a calibrator is a matter of P. De Bievre (&) Kasterlee, Belgium e-mail: paul.de.bievre@skynet.be