This instrument is part of the display of instruments at USGS in Rolla. The shape seems a bit unusual. What was this instrument mainly used for? I assume for higher end geodetic work?
Kern had some of the coolest old instruments. Unfortunately, I was brought up with Wild, so I am no help. That is cool though
Specification wise it is equivalent to a Wild T4 and the uses would have been similar.
The two primary uses were geodetic, including the DKM-3A for astro work, and also used for ultra precise optical tooling applications indoors.
Not quite as precise as the T-4, (I have one of each); it was used in expeditionary geodesy more than for main-line triangulation. I can pick up a DKM-3A; I cannot pick up a T-4.
Long ago swiped by one of my grad students, I once had a booklet published by Kern that was written by some technicians in Italy that did an analysis of the systematic errors characteristic of the DKM-3 with respect to the horizontal circle graduations and the corresponding optical micrometer. The number of observations was unreal; it probably took at least a couple of men over six months of turning angles to come up with the final Fourier Analysis of the errors.