Mark,
Unless I have missed something critical here, my "spin indexer" has normal 10° increment indexes on the primary index ring and 1° increment indexes on the vernier index ring. Thus, I start at the 0° position and move to the (say) 20° position -- and then place my index pin in the (say) 5° vernier hole, remove my primary index pin, and rotate the indexer until the vernier pin drops into the next hole. I have now moved 25° from my initial position. Your 0° vernier hole should index when the primary index pin is in any of the 10° increments. My "spin indexer" is old enough that it has 11 holes on the vernier (0°-10° for double-checking). It is a shop-made tool given to me by a retiring machinist back in the 1960's. I know that I have used commercial "spin indexers," but my fingers know my own tool best.
