No matter if you're turning to an OD, or boring to an ID, the cross feed dial is nothing more than a reference. It's fine for roughing quickly, and it's OK if the callout is +/- .005, but it isn't meant for precise work.
I know someone will say "I can turn/bore to .001, using only the dial" - it is possible on a newer or lightly used machine that has tight gibs, an unworn crossfeed nut, etc. For the rest of the machines, the easiest way to hit a dimension is to stick a magnet-back dial indicator on the cross slide.
This allows dialing off single thousandths, even half thousandths. Even if your machine is pre-WWII, you should be able to do really fine work. If you don't have a mag-back indicator, a regular magnet base will work - it's nowhere nearly as solid, but it will do.
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An ID micrometer is the most affordable & easiest way to accurately measure small bores. Mitutoyo makes a really nice one, but $200 is more than I had to spend. For around $50, J&L sells a ChiWan copy that is usable. Mine often gets used daily, either on the Bridgeport or on the lathe.
IMO, the advantage of an inside mike is the ability to feel bore contact, something that's impossible with telescoping bore gauges. They can either be directly read or read with an OD mike.
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Any caliper, vernier, dial, digital, is much like the graduation on the feed dial -- good for roughing & quickly getting close, not meant for bearing fit work.
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Barry Milton