A combined instrument for general direction finding purposes. The instrument seems to have been derived from instruments used by surveyers. It has a compass, two bubbles for levelling and acurate scales for horizontal and vertical angle measurement. At the bottom is an aiming circle, in use and mounting almost identical to the one for the SF 14. This instrument was mounted on a tripod.

The Richtkreis 31 (RK 31) is the best known type.

We have found a second version.

In 2001 we found the RK 40.

It has a 360 degrees compass with its own bubble.

The bracket houses the bubble for horizontal adjustment.

Otto Fennel und Söhne are the makers.