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Fan scales

A recent discussion with Peter Hopp of Slide Rules fame, prompted by an item in the latest UKSRC Newsletter, finally encouraged me to photograph some of my fan scales. This type of folding laminar scale seems to have been more popular in Europe than it was in Britain or North America – I don’t recall ever having seen one used in a professional context – and they were sold by many major makers including Faber-Castell, Aristo and Linex.

Probably the best known is the ubiquitous Faber-Castell 20/83 of which I have two versions, one with a black leather sheath (presumably the earlier) and the other in green leatherette.

The single-sided blades contain a total of ten reduction factors that seem to be aimed at engineering rather than architectural use, including the perplexing 1:33 1/3 scale.

Faber-Castell 20/83 fan scale labels

They are not listed in my 1988 Faber-Castell English language catalogue, but I don’t know if this is because they had been discontinued, or simply a reflection of their lack of popularity in the UK market.

An exception to this rule (pun not intended) was Blundell Harling’s R280 six-fold sheathless fan scale (my example is a promotional giveaway made for EDM, datable to between 1971 when the firm was founded and 1995 when the telephone dialling code changed). This was supplied in a typical Blundell Harling transparent plastic slip case, as they used for most of their conventional scale rules. It has twelve scales of a more general nature than the Faber-Castell.

Blundell Harling R280 fan scale

A very different approach is taken by this lovely all-steel fan scale made by Chesterman (pre-1963 merger with Rabone) for Monotype, consisting of six double-sided blades engraved with a total of 24 point scales for typesetting.

Chesterman Monotype stainless steel typography fan scale both sides

The construction of this very durable instrument seems to owe something to the fan feeler gauge, a Chesterman staple, right down to the durable leather case that it was supplied in.

Chesterman Monotype stainless steel typography fan scale

A contender for the strangest of all my fan scales is something called the “Allen Miscellaneous Scales” from Houston, Texas, which bears a copyright date of 1949 and was named after its creator, one Kibbee R. Allen.

Allen Miscellaneous Scales open

It offers a vast range of survey and map scales across thirteen fan elements, divided in metres, feet, miles, chains, rods and even varas – a name I had not encountered before, but apparently an old Spanish unit of measurement still used for land surveys in parts of Texas (1 vara = 33 1/3 inches; perhaps this has something to do with the aforementioned 1:33 1/3 scale).

Allen Miscellaneous Scales chains, rods and varas

I was surprised to discover that the Allen scales are still available in the US, although appear to have been discontinued according to one vendor. Likewise, metric fan scales can still be had from Blundell Harling who do a nice promotional version with a very comprehensive scale set (though not quite as comprehensive as the Allen scales!)

The earliest example of a fan scale that I have come across is from the Wichmann catalogue of 1904-5, listed as “No. 432 Fächermassstab” (trans. fan scale) with ten folding card scales. This design was apparently protected by a DRGM patent, which I have not yet been able to locate.

Wichmann’s fan scale appears to have been first introduced in 1903, based on a review found in the journal Praxis des Fabrikbetriebs: Supplement zu Uhland’s Technischen Zeitschriften which ran a monthly column “Für Kontor und Zeichenbureau” (for the office and drawing office). It describes Wichmann’s new Fächermassstab as an attempt to overcome the limitations of traditional flat and triangular rules (small number of scales, unwieldy, divisions become illegible over time, celluloid cracks off). However, the reviewer was not entirely convinced by Wichmann’s implementation of the design, suggesting that it would be better to use canvas paper or celluloid strips instead of cardboard, or else that the cardboard should be varnished to prevent staining. The accompanying illustration is the same one that appeared in Wichmann’s 1904/5 catalogue.

Wichmann No. 432 Fächermassstab fan scale 1903 illustration

I have also found a similar fan scale from around the same time, named the Hafried-Fächermassstab and very similar in layout to Wichmann’s. Hafried Verlag was a Hamburg stationer and publisher of technical literature in the early twentieth century, named after its founder Hans Friedenberg. Their scale has twelve segments, as opposed to Wichmann’s ten, but looks otherwise similar enough to suggest that they were from the same maker. Whether this was Wichmann, Hafried, or someone else entirely remains to be seen.

Fan scales are also known to have been supplied with some planimeters in the USA, such as the Lippincott fan scale, kindly brought to my attention by planimeter virtuoso David Green (see section 10.3 of his excellent survey of Willis and Lippincott planimeters here). Sets of short boxwood scales for measuring the height of steam engine indicator diagrams were often sold with the indicators themselves, scaled to match the different springs included in the box. A planimeter could then be used to calculate the area of the diagram, which represented the overall efficiency of the engine being measured. In a way, it seems a natural progression to join together these short and easily misplaced scales – a bit like having a set of linked measuring spoons in the kitchen drawer.

The main problem I see with fan scales in general is keeping the edge of the scale flat to the surface being measured, which explains why all of the (moderately) successful designs have thin, flexible laminar blades with a flattish rivet fixture. As the number of blades increases, the overall thickness of the stack also becomes problematic. This is probably why the production version of Wichmann’s fan scale had five single-sided scales facing in each direction, in contrast to the catalogue illustration which shows all of the scales facing the same way.

Wichmann No. 432 Fächermassstab fan scale

It would be good to discover who first came up with the idea of a fan scale and when. If anyone knows of earlier examples than Wichmann’s, I’d be glad to hear about them.

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