I find the accuracy of a veneer caliper extremely helpful when dealing with measurements like the fork crown race on older bicylces and headsets, which can vary slightly depending on national measurements. But then I work largely on older bikes, and as the good reverend notes, you can run across some odd sizing issues on them. I deal with them on a daily basis. I suppose if you're working only on newer stuff, it becomes less of an issue, so a standard caliper should do the trick. You can pick up a general caliper at your local Home depot as well.
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