Mitutoyo DRO

For a detailed description of the measurement method used in Mitutoyo
calipers, see US Pat #5973494--Electronic caliper using a
self-contained, low power inductive position transducer .

See http://patent.womplex.ibm.com/details?pn=US05973494__ on the IBM
patent site.

In general, you can find all kinds of good technical information in
US patents since an inventor must disclose enough information for
someone "skilled in the art" to understand the invention. I did a
search for Mitutoyo under assignee. The IBM site has full image
patents starting from the early 70's.