This text focuses on the invention of the Vernier, a very useful instrument in Engineering and used to measure fractions with great precision on a scale. Invented by Pedro Nunes at the time of the development of the great Portuguese navigations in the XVIth Century, its improvement by Clavius led to the development of the calliper by Vernier. In 2002 the 500th anniversary of the great Portuguese engineer Pedro Nunes was celebrated and his invention of the Vernier is remembered. Understanding the foundations of such a technological tool is a means of justifiably honouring him.. Beyond this honour, this historical study can give us an idea not only about the working of this important instrument but also serve as an illustration of the intimate relationship between scientific concepts and the social fabric around them. Such a historical study may also lead us to an interesting way to illustrate the educational problem of the representation of fractions.
History in Mathematics Education; Vernier; Calliper; Pedro Nunes