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You can see them fairly often on e bay, called the #246 "Ultra Mike" Micrometer / Comparator; cost $495 in 1970 according to my Brown & Sharpe STM-5 catalog. 0-4" range direct reading to one tenth of a thou. and comparative measurements to 50 millionths. If equipped with an electronic gage head instead of the dial indicator, comparative measurements to ten millionths.
We've got them on anything big/expensive enough to be considered an accounted capital expense at work. Basically a tag with an ownership stamp (eg property of company blah) and a serial number for accounting to keep track of where the item is and when it enters and leaves service. Ours are usually stamped with a reminder to turn the tag in if the asset is scrapped or not to scrap the asset without notifying accounting