The Fowler "twelve-ten" (the name seems to come from the fact that, while one set of logarithmic scales is divided into tenths, like on a normal rule, the other's divided into twelfths. i'm not sure what the purpose of this was. it's possible it had to do with dealing with inches, but that seems a bit weird) is pretty typical of the pocket-watch style rules made around the first half of the century. The rule has two cursors, one fixed and one controlled by the knob at the 2 O'Clock position. The knob at the top of the rule rotates the face of the rule. To multiply, you turn the moving cursor to one factor, turn the face until the other is under the fixed cursor, and read the result at the moving cursor. Besides the weird twelfths scale, this one has the usual trig scales and a bunch of gauge marks around the outer scale for things like metric conversions, Pi, and degree-radian conversions. It's awfully cool, probably my current favorite slide rule. It really feels like a high-quality instrument; it's got a nice heft to it, and seems really well-made. They're spendy, but if you can lay hands on one, it's worth it.