Transversal (instrument making)

Transversals are a geometric construction on a scientific instrument to allow a graduation to be read to a finer degree of accuracy.

In 1342 Levi Ben Gerson introduced an instrument called Jacob's staff (apparently invented the previous century by Jacob Ben Makir) and described the method of the transversal scale applied to the mentioned instrument.

In the interim between transversals and the vernier scale, the nonius system, developed by Pedro Nunes, was used.

[1][12] Diagonal scale follows the principle of similar triangles where a short length is divided into number of parts in which sides are proportional.

Diagonal scale is used in engineering to read lengths with higher accuracy as it represents a unit into three different multiple in metres, centimeters and millimeters.

In addition, a linear transverse line will not divide the radial grid into equal segments.

Tycho Brahe created a grid of transversal lines made with secants between two groups of arcs that form two graduated limbs.

[16] While Abd al-Mun'im al 'Âmilî (16th century) drew them all in the same direction (although his instrument has less precision).

[17] The method of the "straight transversals" applied to the measurements of angles on circular or semicircular limbs in astronomical and geographic instruments was treated by several authors.