Aside from the one in our collection, we know of two others; one is in Glenn Henry's collection and one is on the USS Slater (now a museum ship).
Glenn Henry has a MARK 6 Mod. 16 Serial No. 1416 along with lots of other great computers. (Note the slight change in the naming of the computer. Glenn's computer is designated a Mark 6 while ours is called a Mark VI.)
Although the computer controls and output look almost identical to the one in our collection, there are four significant differences.
The Mark VI on the USS Slater is mounted on a wall in an inside room...it was likely moved there since it DOES have the Sighting Vane mount.