Molter

The Molter is sort of a cheaper version of a Halden Calculex. The mechanism is basically the same, though the case is different - lighter for having substituted thin celluloid for the Halden's glass. But it's a simplex with fewer scales, and a great deal less elegance.

Here are the parts:

The dials are fitted back to back, and held between the thumb nuts. One nut is keyed to the inner dial of one side. The other nut screws into it and is locked in place with a set screw that goes through the keyed nut from the outside. The dial assembly gets sandwiched between the metal outer rings, which bear lips that nest one in the other.

The inner dial of the moving side fits into the outer dial, with a keyed washer between them. Both are paper glued to concave circular plates.