The two-cylinder M-4 has been known by the following names: Kroeber simply and later Kroeber & Koller. But the engine on display at the Munich Museum has the name “Dr. Kroeber & Sohn GMBH ”.

“Dr. Kroeber & Sohn GMBH identification plate”

“The mentioned M4 engine in Munich” (E-V.)

-This engine is mutilated by the lack of a carburetor and a complete ignition.

-Dr. Kroeber & Sohn refers to Dr. Kroeber and Son. The author does not know at what time he joined Köller, or if Koller was his son.