Mysterious calculating instruments

Members of the KRING regularly encounter calculation instruments whose origin or use is unclear.
Can you help us solve these mysteries?
Mail your information to @ Click on the images for a larger version.

… Nato stocknr: 6B-5036 / Doc.nr 680701 / Inspectiedatum 4-1-61 …

A solar compass? For a Starfighter?
Both the Zonnewijzerkring and the Kring Historische Rekeninstrumenten can't figure it out.

See: Andries de Man, “Instrument for Starfighters” MIR 91 p.31
KRING-member Meine van Essen solved this mystery. See the upcoming MIR.

… Aristo 10063, designed in 1951 by Dr. Ing. Luetgebrune for Continental …
Is this a slide rule for tire design? How does it work?
Is it related to the Aristo 90187 Reifenrechenstab?
See also: Klaus Kühn, Karl Kleine, “Dennert & Pape, ARISTO 1872 - 1978” & animation

… 17th/18th century abacus from the Gdansk National Museum…

Is this really an abacus?

See: Henk Peters, “Mystery object: an abacus?” MIR 75 p.12–14

… the enormous collection of the Land Registery Museum contains this small black slide rule…
Where does this slide rule come from? What was its purpose?
Is there a reason the slider can only slide to the left??
See: Otto van Poelje, “Mystery black slide rule in the Land Registery Museum” MIR 61 p.20-22

… a hardboard pocket slide rule …

Who made this strangely sized pocket slide rule from an unusual material?
Does this have anything to do with the “Demoulin” company? Or with Graphoplex?

See: Otto van Poelje, “A puzzle for readers” MIR 59 p.10-11

… cercle mystère …

Prototype? One-off? Do we see the hand of Paul Pouech?

See: Ronald van Riet, “Mysterious Circles” MIR 58 p.32

… linear non-linear scales …
Why would you do trigonometry for only three specified radii?
See: Otto van Poelje, “Mystery ruler from Kleman with transversal scales for sinus and chord” MIR 55 p.21-22