Angle meter with several transversal measuring rods

The protractor with several transverse map scales is dated from the 19th-century, as indicated by the engraving "Lewert in Berlin" (pointing to the instrumentmaker Carl Friedrich Lewert (1807-1889)). It comprises threemeasuring instruments: On the left and on the right of the big square are rulers, on top of the big square six transverse map scales are engraved and the semicircle allows the exact reading of angles within a half degree.

The semicircleprotractor has five scales. On the inside the degrees from $10$ to $180$ are marked in counterclockwise direction , in the second semicircle the degrees from $190$ to $360$ are marked, again in counterclockwise direction. On the third semicircle the degrees from $10$ to $180$ aremarked again, this time in clockwise direction. Located on the fourth semicircle are dividinglines for the singledegrees, and on the outside these single degrees are bisected again, so that the size of an angle can be exactly read off to a half degree.

In the past, transverse map scales were used to transfer a distance from a map into reality without a calculation. With a compass, a distance on a map is recorded, afterwards the compass is inserted horizontaly, so that the other compassleg is lying on the edge. First the vertical line is read, then the slanted-vertical (transverse) one and then the horizontal one. The sum of these numbers specifies the length of the distance.

Text written by: Aline Weinert