April 8, 2008 3:15 PM   Subscribe

What are those circular disc things that you rotate to look up information? Volvelles.

The definitive book on the subject is Jessica Helfland's Reinventing the Wheel. The first volvelle was created by Benedictine monk Matthew Paris in 1250, to save rotating an entire book around. Most volvelles, historically, were designed for astronomical purposes. Recently we had an FPP about Ramon Lull, who seems to have been one of the earliest users of volvelles for purposes other than astronomy.

Nowadays volvelles (or wheel charts) are rarely seen, but they were very popular between the 30's and 60's, the heyday of slide rules, before the invention of electronic calculators. The addition of multiple circles makes the volvelle capable of greater complexity, and they are ideal for codes and ciphers (Thomas Jefferson's cipher wheel, which is isomorphic to a 26-layer volvelle). Here is a description of the volvelle that came with the game Bard's Tale III in 1987 including a zip file with scans of it. For comparison, here is the complex table it equates to. More recently, the game HeroClix makes use of volvelles, as the combat dial base of the character miniatures.

So, how to make your own volvelles? Here's an example of one (PDF). Here's a program for making simple two-layer volvelles, which I have tested and works, although it's probably better just to print out the example volvelle, work out how it works, and stick it to a paper plate. Or make this one. (More paper plate volvelles.)
posted by aeschenkarnos (12 comments total) 18 users marked this as a favorite
(My thanks to misteraitch, who provided the necessary word.)
posted by aeschenkarnos at 3:16 PM on April 8, 2008

Funny; I'd seen them, but never knew there was a word for them. I saw one last week in one of those hipster novelty shops comparing religions (Mormon, Scientology, etc.) listing perks and problems for each one...pretty funny, although I doubt many people find them funny enough to buy.
posted by kozad at 3:21 PM on April 8, 2008

Worst design job ever - trying to copy a body mass index volvelle for a client. It's a logarithmic scale (or at least not regular) with lots of divisions. Blergh. Thankfully I was only managing the poor sod who had to do it.

Nice post and a new word for the day.
posted by i_cola at 3:27 PM on April 8, 2008

Great post! I have one of these hanging on the wall.
posted by Armitage Shanks at 3:30 PM on April 8, 2008

Nice post, and I always enjoy a new word. These are actually pretty common in medicine usually with the name of a drug on them and used for such things as calculating BMI (as i_cola noted), dosing drugs, and most commonly calculating due dates for pregnant women.
posted by TedW at 4:21 PM on April 8, 2008

They're still used in the aviation field, too, although I've always known them as circular slide rules. The trusty E6-B is what every student pilot learns to use to calculate fuel burn, time en route, and other pertinent flight planning information.
posted by backseatpilot at 4:25 PM on April 8, 2008

Hey, HackMaster (D&D-like roleplaying game) uses one of these for its Combat Wheel.
posted by hjo3 at 4:50 PM on April 8, 2008

The Department of Energy's book "Effects of Nuclear Weapons", which was popular with my deluded survivalist buddies in the '70s, came with a great wheel calculator tucked in a little paper pocket inside the back cover that let you dial in megatonnage and distance and told you radiation, heat, blast-wind speed, overpressure, and I forget what else. Hours of fun - I wonder where mine has got to...
posted by nicwolff at 5:25 PM on April 8, 2008 [2 favorites]

Wow, I linked that without realizing that the little forms on that page render the wheel itself, all dialed-in to the values you entered. Neat! And I forgot that one of the results it gives is crater width and depth, awesome.
posted by nicwolff at 5:27 PM on April 8, 2008

It's nice to see them used for slide-rule type calculations and not just wine/food pairing, or other things that might as well be a table.
posted by BrotherCaine at 6:31 PM on April 8, 2008

hjo3: Hackmaster, as it is wont to do, stole the idea from the TSR original.
posted by faster than a speeding bulette at 7:06 PM on April 8, 2008

I used one of those in my graphic design classes for proportional scaling, e.g. 11.25" -> 13" = 115% increase. (Had to dig it out of a box to provide that example.)

There's something very satisfying about using them. But then, I also miss the card catalog.
posted by rifflesby at 10:41 AM on April 9, 2008

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