FC 366 prime numbers slide rule – Fantastic Vintage Finds
Sometimes items find me…I bought this slide rule from a bad picture. A picture taken from afar because there were 30+ slide rules in it. I mostly bought it because I noticed the cursor. Not only a strange set-up with the table joined to the window frame, but also very familiar looking. At least to me…
The cursed cursor (…or not?)
…and perhaps to some visitor to the Vienna Museum of science and technology for they seem to have one (not currently on display but you can find it here). Yet having it in a museum collection does not mean a thing when they do not underline the significance of the piece. Also Faber Castell seems to have a specimen in their archives…but I guess they have most of the models they produced in their archives (hopefully). This is what the cursors look like.
When I just had the loose cursor (the lower one in the picture), bought in a small bunch of 10 cursors still in the factory fresh boxes from the 1960-1970…I did not know where to look for information on it. The cursor does not have a manufacturer’s name on it and it was much earlier than the others (by Nestler and Aristo) and it did not fit the 3 additional slide rules either. Nestler does have some catalog pages on their earlier exchangeable cursor program from the time you could upgrade your cursor to fit your needs.
Also the Faber Castell book by Peter Holland (in co-operation with Dieter von Jezierski, Günter Kugel and David Rance) has an in-depth overview of cursors and their compatibility. This book has kindly been made digital and provided to interested parties for free…for which I am very grateful…you can find it here (chapter 12 deals with cursors). Unfortunately the 366 cursor is not shown, and even more interesting they authors mark it as interchangeable…which it is not…for you need the table on the cursor when operating the slide rule as per the Faber Castell DRGM 344576 from 1908. See below where this great cursor would help with reading the table on the 366 cursor, I am not sure it was ment to be attached to the existing cursor….if it would…that would be great of course!
So how was I supposed to find out to which slide rule this cursor belonged? .I just put it away but only only for a few months…because the entire slide rule with cursor crossed my path and I was looking forward to finding out. I had no idea how special this cursor and slide rule were.
The slide rule to end all (logarithmic) slide rules
This is what it looks like from a little further away. It seems there are only 2 sets of scales. Bottom one could be logarithmic but the top one sure is not…weird.
Nothing on the back. Nothing on the back of the slider. But there is a strange little table on the cursor as we already established. Beautiful made, can wel be reddish pearwood (first model run was in the lighter boxwood). It also seems to have an inch and mm scale on the small sides as well as wooden dowels to keep the white fineer in place. Both box and case boast the DRP patent nr. 206 428 for the metal spring rings in the body. I later learned also 2 DRGM claims were in use but Faber Castell only (could prolonging) state DRP patent numbers. If you want to know what the difference is between a DRP and DRGM read this interesting article.
So I now I had the number 366 on the slide rule to go by…and it lead me to where I should have started…my trusted fellow collectors from the Oughtred society. Via the wikipedia article on the 366 (wow did not even know specific slide rules made it in there)..I got to the in-depth article written in 2004 by Dieter von Jezierski, Detlef Zerfowski and Paul Weinmann (thank you very much) called FC 366 a very unusual slide rule.
Dr. Schumacher was a German professor who took it upon him to use the idea of the slide rule (both shaped straight and circular) to a different approach. Out the door with the logarithmic scales (the entire concept to which all mathematics slide rules were held)…and created a slide rule to be used with prime numbers instead. The ease of working with real numbers in prime fields was a bit downplayed by the additional need of the table and then still it was only usable for a smaller set of prime numbers. Please read the article mentioned above for a full explanation.
This was a completely new approach and must have spiked the interest of Faber Castell who did not want to miss out if it might be a succes. The slide rules concept was entered into the German DRGM for a 3 year registration (but not officially patented) and was build to the highest standards using the new construction methode from 1907 and 1908 to be released to the public (after a first run of test models in boxwood) in 1909 in Pearwood. Sales were low and after 20 years it was discontinued completely. The logarithmic approach stood tall and the 366 became an oddity…but what a nice one.