Circular slide rules have two advantages over straight slide rules. They have a longer scale length for the same footprint. A 10cm diameter circular rule has the same length scale as the straight rule of about 30cm. The second advantage is that they have a continuous scale, which reduces the number of manipulations.

The central disc is rotated on its axis by means of the knob on the back of the instrument. This instrument can perform multiplications, divisions and cross products.

Note that the graduation system is pretty simple. One distinguishes only three scales.

Two of them, located on the central part, correspond to the numbers and their reciprocals.
The size of the instrument gives a scale of a length of about 80cm.

K. Emil TRÖGER produced calculation disks in different sizes, as well as calculation tables.

Some of his instruments are dedicated to specific professional needs.