While not exactly a slide rule, this device operates on logarithms and moveable scales so I've decided to include it here.
This device has scales and fixed indices on both sides of it, and a moveable index on one that's linked to the scale on the opposite side. The two knobs control the two moving scales.
Thanks to the kindness of several folks, I now have a reproduction of
the owner's manual and a wealth of other data on this device. Fowler's
manufactured at least three different models of calculator; the one I
have is the "Vest Pocket Long Scale" model, the others were the "Universal"
and the "Magnum". I'm still digesting this, and once I get a decent
handle on it will post my own set of instructions here.