High-precision carrier

With this model it is possible to read off, or draw in angles to the exact arc minute, as wel as clockhoursand -minutes on a drawing.

It consists of two semicircles with a mobile slider, which may be secured with two screws. On the external semicircle the degrees from $1^\circ$ to $180^\circ$ are marked, every degree is divided into three pieces. With the slider it is possible to read the degrees to $20$ arc minutes exactly. Marked on the inner semicircle are the clockhours from $1$ to $12$, between every hour there are $15$ other subdividing lines.

If the slider is moved, a so-called Vernier scale also moves in between the semicircles. On the Vernier scale there are other lines, which enable the exact reading of arc minutes or clockminutes: If the zero-point does not match exactly with a line on the scale of the favored semicircle, it is necessary to count the number of lines on the Vernier scale to the first point, at which a line of the Vernier scale and a line from the other scale match exactly. This number gives the number of minutes, additionally to the one from the scale of the semicircle.

The words "R. Rofs. " and "Essen-Ruhr ", at the bottom of the model, could be a reference to creator and place of origin of the model. The protractor was probably produced in the late 19th-century.

Text written by: Aline Weinert