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Sketchy calculation

As a bit of weekend fun, here’s something called a Rechenstift – German for “calculating pen” – by the venerable Hamburg firm of Dennert & Pape, erstwhile inventors of the laminated celluloid scale and better known today by their brand name Aristo.

Aristo 6103 Rechenstift slide rule pencil four view

Produced around 1960, this bizarre hybrid device came in two flavours: the Aristo 6101 ballpoint pen and 6103 clutch pencil for standard 2 mm leads. I was fortunate enough to find a copy of the latter (ballpoints are a bête noire of mine) and one in reasonable condition for its 60+ years. Both versions are listed in a 1961 Aristo catalogue, which is the only source I have found for their product numbers – the pencil itself is unmarked, save for the ARISTO logo.

Aristo 6103 Rechenstift slide rule pencil 1961 catalogue illustration

The design was protected by a utility patent filed in May 1959 that can be seen here. It presents two versions of the Rechenstift, one identical to the production version and an alternative three-sided variant with two sliding faces and a wraparound cursor. I have not seen this second version in the wild, although the same could be said of the production model until I came across mine.

Aristo 6103 Rechenstift slide rule pencil patent drawings

As noted out in this blog post by the HNF (Heinz Nixdorf computer museum) a major drawback of D&P’s design is that the slide rule and the pencil could not always be used at the same time, as for some calculations the slide would project beyond the point of the pencil. Worse still for the lefties among us, the slide rule is only upright when the pencil is held in the right hand.

Aristo 6103 Rechenstift slide rule pencil sliding

Another problem that I have found with the design is that the slide is extremely stiff, to the extent that I did not feel comfortable moving it any further than shown in the image above for fear of breaking the plastic. It is unclear whether this is a result of Aristo’s patented spring friction device (indicated by label f on fig. 2 of the patent drawings above), or else simply due to the age of the pencil. The minimal captive cursor with its single red hairline is almost as stiff as the slide.

Aristo 6103 Rechenstift slide rule pencil cursor detail

I expect the main function of the Aristo Rechenstift was as a promotional tool for their slide rule business. As a pencil it is too unwieldy for serious drawing purposes, and the small form factor severely limits its usefulness as a slide rule. Even so, it is a rather beautiful synthesis of two technologies that were rapidly heading towards extinction.

Aristo 6103 Rechenstift slide rule pencil revese

While the slide rule elements bear the hallmarks of Aristo’s manufacture, it would be interesting to know who made the leadholder parts for them. It has something of the look of this pencil from Ero, a company that also made pens (and pencils?) for Rotring around this time.

Ero Ernst Rodenhäuser mechanical pencil

Rotring also collaborated with Aristo from the 1970s, before eventually acquiring their fellow Hamburg firm. However, it would be good to find some more concrete evidence to support this idea.

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