The top dial is for the cross slide on my 1941 South Bend lathe. The bottom one is for the compound. If you look close, you can see they are different scales. The cross slide feed screw was changed from the factory 10 threads per inch with an indirect reading dial, to an 8 thread per inch screw with an direct reading dial. For the cross slide, the direct reading dial is a little easier to work with. For every turn of the handle, the tool moves in 0.125 inches, but would REMOVE 0.250 inches off the diameter. You would rarely, if ever, measure the RADIUS of the part you are turning, so this configuration makes the math much easier.
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