Gauge blocks

   Am I really going to need to allow for millionths of an inch ? I'm looking at an 81 piece set from Shars , a grade B with the deviation table for under a hundred bucks . Looks like the biggest variance is .000034" , or about a third of a ten thousandth . I can't see any project that I might get needing that kind of precision ...
   I'm considering buying the set just because I've kinda wanted some and I think they'll get me closer to perfect in my upcoming depth mike project . Since they can trace back to a national standard I can also use them to check all my other micrometers , none of which have been calibrated for at least 40 years , and in some cases longer than that .
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Snag
  It's great to be straight !