Lord's

I really don't know what this calculates, but I love it! It has 1 fixed outer ring that surrounds 2 movable inner rings and then a fixed hub. So maybe it does some sort of cubic operation? Peter Hopp's book on pocket watch slide rules only says it "appears to have been designed and made for mill managers in the spinning and weaving trades to be able to make specific relevant calculations." If anyone knows what calculations those might be, I'd love to hear from you.

This is about 65mm across, all metal and heavy! It doesn't have a glass, and I'm not sure if it ever did, though it seems likely. I'm not surprised, though. There's precious little "lip" to hold a glass in place.

Curious to know what's inside? Take a look:

The largest, outermost ring is attached to the case via 3 tiny screws. Its inner edge laps over the outer edge of the larger inner ring, holding it down as well. Then, the smaller inner ring similarly laps over the larger one, and is held down by the hub which is attached from the rear with the 3 brass screws. Note that these screws fit through the 3 slots in the case, such that the hub can be adjusted through about 60 degrees.

The two stems turn gears that engage racks on the backs of the two inner rings.

A big but faint "3" is scribed into the inside of the back cover. I wonder what that's about.