Yesterday, while walking a bit around Zurich with A. Saha (one of the new postdocs, who will arrive at ETH in September) I found a slide-rule in an antique shop; since I had never actually seen one before, and it was very cheap, I bought it immediately. It is in very good shape, and seems to be fairly sophisticated, and I hope to learn a bit how to use it for the fun of it.
I was interested to see that π is indicated on some of the scales, but then we also noticed another mark indicating a value between 1.74 and 1.75, highlighted by a symbol which I had never seen before (click for larger picture):
Trial-and-error led us to the conclusion that this number is simply
and so is to be used to convert between degrees and radians. Further searches revealed a number of pictures of (essentially) identical slide-rules with a small tick to indicate this constant. However, I haven’t found a picture yet with the strange symbol. Is it really standard? Has anyone seen it before? Is it somewhere in Unicode?
Probably comes from “g”, as in “grade”, as in “degree”.
“ro” greek means “radian” proposal from Boris Apsen an engineer from exYugoslavia:
“ro” x very litle angle = sin or tan of this very litlle angle
That sign there is onthe faber castell 111/54 ….
I think it is an oddball variety of Greek rho. IIRC my slide rule has a similar symbol. I’d have to dig it out and check… it even comes with a manual, so the symbol might be described further.
You might be interested by this site
http://sliderulemuseum.com/
containing dozens of pictures of slide rules…
#1,#2: the symbol also reminds me of either “g” or “rho”; but “g” for “grads” seems strange to me since there are 400 grads for 2π radians. “rho” could be for radians.
#3: Yes, the “sliderulemuseum” has a few pictures of the same model as mine, though without the bizarre rho/g symbol as far as I can see…
I own a Faber-Castell Novo-Duplex slide rule that shows this symbol on several scales. The “Rechenstab-Anleitung” coming with this slide rule uses a rho from a normal greek font (and not a handwritten one as on the rule itself). It seems that this mark is mainly intended for calculating sin and tan of small angles.
It’s probably just a rho, as Christian Blatter says. However, the symbol as printed looks a bit like the Unicode character U+018D (LATIN SMALL LETTER TURNED DELTA = reversed Polish-hook o), ƍ if your browser supports it. It’s apparently an old phonetic symbol (“labialized alveolar fricative”, whatever that sounds like), so I’m guessing the similarity is just a coincidence.
It’s true that it definitely looks like that Unicode symbol, but I agree this must be a coincidence (if I turn the slide rule upside-down, it looks a bit like a Greek delta but not that much; or similarly, it does not look that much like an a lowercase “o” with a hook or cedilla).
I posted a similar query today at http://530nm330hz.livejournal.com/325716.html, and one of my friends found this page. If you get a definitive answer, let me know, and if I find out, I’ll follow up here!
Thank you.
You solved the 45 year riddle of what that character represented on my dad’s slide rule.
That mark appears on the C and D scales on both sides of my recently-acquired Faber Castell 2/82 N rule, and also on the CF & DF scales.
According to the FC English instruction manual, in the “Interpretation of scale marks” section on page 25, this mark is ϱ (rho) = pi/180 = 0.01745.
For whatever (Germanic) reason the character looks like the Roman character ‘g’.
The mark in question is detailed on this page: “http://osgalleries.org/journal/pdf_files/18.1/V18.1P56.pdf”. This page is quoted from the Journal of the Oughtred Society.
This “backwards Rho” symbol, representing π/180 (or perhaps 2π / 360) apparently originated with the Dennart & Pape company in 1926.
This version of the Rho symbol is common on Faber-Castell Duplex slide rules, such as the 2/82 and 2/83 models.
corrections…
The mark in question is detailed on this page: “http://osgalleries.org/journal/pdf_files/18.1/V18.1P56.pdf”. This page is quoted from the Journal of the Oughtred Society.
This “backwards Rho” symbol, representing π/180 (or perhaps 2π / 360) apparently originated with the Dennert & Pape company in 1923.
This version of the Rho symbol is common on Faber-Castell Duplex slide rules, such as the 2/82 and 2/83 models.