Having used digital, dial and Vernier (manual) caliphers I have to vote for the manual/vernier ones. They are just as accurate as digital or dial, don't need batteries and are, IMHO, far more durable. It doesn't seem to take much of a shock to wreck a digital or dial one and good luck trying to re-calibrate it if you can even get it working again.
The manual ones aren't impervious to damage but, if not completely ruined, one can usually restore and recalibrate one. One way to prevent most scratching with a steel calipher is to take very fine (600 grit or more) and gently round and smooth off the sharp edges of the jaws--not the end points, though. Avoid sanding or polishing the flat measuring surfaces of the jaws as this will change the distance between them. If one is very carefull and has the right equipment one can even polish these rounded corners with tripoli or Fabuluster. I believe that Grizzly Imports sells a good one for under $20.00. I'll try to find a link.
http://grizzly.com/products/6-pc-Measuring-Tool-Set/G9790
The only manual one that I could find online with Grizzly is as part of this set of measuring tools. It's a good deal, I think if one needs all that. Their headquarters & main showroom are here in Bellingham and I've purchased two of these caliphers there. Next time I get up there I'll try to remember to see if they still have them. I would suggest calling or emailing them and asking.
Just found vernier caliphers listed for $10.22 USD at:
http://mcmaster.com
They are item # 2192A21 or enter "vernier calipers" in the search function and scroll through. I'm not familiar with the company or product, though.
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Marc
http://www.flyrodjewelry.com/home.html