I recently bought an inexpensive, 4-inch rotary table for use with my mini-mill. While I learned to read a vernier scale when I was about 12, this one has me stumped.

Each division on the moving dial is 5 minutes (12 divisions between degrees, 60 minutes/degree, 60 / 12 = 5 minutes). But how to read the vernier? There are + and - six increments, so I think the total range is dividing the 5 minutes of each graduation of the moving dial into 12 parts, or .4166667 minutes per graduation. That happens to be 25 seconds per graduation, but so what? If you get alignment with either of the "60" marks on the vernier, that would be 2.5 minutes. But what about the others; why the very odd value? And why is the 2.5 minute mark on the vernier labeled "60"?

Something tells me that each vernier division should be 0.5 minutes, but damned if I know why, or if that's true.

Any help would be greatly appreciated. Thanks, guys!