Unusual Item: Circular Slide Rule

Circular Slide Rule

Here's a unique item to include in a 17th century setting. At first glance it appears to be an unusual brass pocket watch, but it is actually something even more rare. The item is brass and 3" in diameter, but it does not tell time. It is a prototype brass circular slide rule designed by the Englishman, William Oughtred. The different circles can be rotated past each other. Scholarship (especially mathematics) and Savvy will be useful for figuring out what the 'watch' does. A slide rule would be useful for all sorts of mathematical operations and rapid calculations. In game terms it should provide a bonus die or better to a career for many tasks e.g. Sailor/Pirate for navigation and map making, Soldier for constructing large fortifications or siege lines, Scholar for Astronomy and almost any mathematical operation, possibly even Spy for encryption and decryption.


Oughtred's Circles of  of Proportion

I like including bits of period high tech. In my campaign the slide rule showed up as a result from a solo adventure using Rory's Story Cubes. The Story Cubes served as the starting point and some Internet browsing turned up the history of the slide rule itself. One of the player characters ended up with the item as a result of a street fight. Although he didn't recognize what it was, a PC who was a scholar did. Eventually the PCs turned the unique item over to the Society of Jesus.

This slide rule could serve as a McGuffin sparking an adventure either to steal or recover the slide rule or the party might guard, kidnap, or rescue the inventor, William Oughtred. For a clock-punk or fantastic setting, perhaps Oughtred has developed an even more powerful device - possibly some sort of early difference engine.