Notes: "The K&E Universal Slide rule first appeared in 1900 and was in their catalog until 1909. It was designed to solve the problem of how to put more scales on the face of a slide rule when your dividing engines can only cut scales on the edges of the stators and slides. Solution: more edges, hence three stators and two slides, although the “two” slides are connected and therefore a single slide. The L scale is in the middle of one slide rather than on an edge, leading to speculation that K&E could cut linearly divided scales in the middle, but not non-linear scales. The Universal is quite thick compared to other K&E slide rules, and the reason is the strip of wood connecting the “two” slides; it cuts the thickness of the center stator in two. To make the center stators strong and rigid enough, the whole rule had to get thicker. The Universal is quite rare, only 5 are known to exist. The reason for the rarity is probably cost. The 25cm Universal cost $20 in 1900, which is $605 in 2019 money. That’s a very expensive slide rule indeed. The Universal was discontinued after K&E had the capability to cut scales anywhere on the slide rule, not just on edges."
