Nonius (device)

Technical features

The nonius was used to improve the astrolabe's accuracy. This consisted of a number of concentric circles traced on an instrument and dividing each successive one with one fewer divisions than the adjacent outer circle. On a standard scale of 90 degrees, there are an additional 44–45 concentric circles, with each divided into a specific unit size such that a scale unit on position n had an arc of 90/n degrees. Thus, the outermost quadrant would comprise 90° in 90 equal divisions, the next inner would have 89 divisions, the next 88 and so on. When an angle was measured, the circle and the division on which the alidade fell was noted. A table was then consulted to provide the exact measure.

Applications

The astronomer Tycho Brahe applied the nonius to the astronomic quadrant.

In numerically controlled machines, the nonius is part of several absolute encoders, that measure linear or rotational displacements.

References

References

1. (2015). "Pedro Nunes". Infopédia [em linha]. Porto: Porto Editora.
2. (25 July 2004). "Diagonals and Transversals: Magnifying the Scale". Journal of the Oughtred Society.
3. (June 2021). "The Nonius".
4. António Estácio dos Reis. "O conceito de nónio". Ciência Viva.
5. António Estácio dos Reis. "Tycho Brahe recorre ao nónio de Pedro Nunes". Ciência Viva.
6. "Nonius interpolation provides excellent differential linearity and higher resolution for linear displacement measurement systems or rotary encoders".