Nonius Display remarks
The question of what a nonius is came to the fore when the term in the user manual of an oscilloscope software led to an unexpected historical investigation. The term appears in the GOWIN manual. In the manual, the vertical red lines located at positions 139 and 200 on the waveform display are called “nonius,” and the figure bears the caption “Figure 4-7 Nonius Display (Standard Mode).” To delete the line, the user is instructed to select the nonius and right-click, then press the “Remove Marker” option. In this usage, nonius means a cursor or a marker line.
Pierre Vernier figures
The roots of the term reach back to the history of measurement. Pierre Vernier developed the vernier scale, which allows values to be estimated more precisely, in 1631, but the Portuguese navigator Pedro Nunes had used an earlier version of it on astrolabes in 1542. The Latin form of Pedro Nunes’s name was Petrus Nonius. The term was given in reference to him.
The nonius consists of concentric circles.
The table in the field
Each circle on the instrument contains fewer divisions than the one before it toward the center. While the outermost ring has 90 marks for 90 degrees, the next ring has 89, and the one after that 88 marks. The alidade cuts across these circles. One checks which mark on which circle the astrolabe’s line called the “alidade” is closest to, and the correct value is read with the help of the table. In an example from Nunes’s own system, the line, on the 65th
John Calvin measurements
circle passes over the 27th mark, and using the table, the value 37º 23′ is found with a precision of 0.08 minutes.
Nunes was considered one of the greatest mathematicians of his era. However, Charles V, Nostradamus, and John Calvin, who were born in the same period, are far better known than he is among the general public today.
The reason for this is presumably a translation mix-up. The Chinese term 游标 can mean both a computer cursor and a vernier/nonius, and it appears that the wrong English equivalent was chosen as a result.