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Dual-reading calipers with Imperial/SI units on same dial
silvermandualdial.jpg
DualDialCaliper.jpg

I don’t know how long they’ve been available, but Timothy J. Silverman’s lovely photo (uppermost) just alerted me to the existence of these dual-reading dial calipers that simultaneously report inches and meters on the main scale and the dial. I do remember wanting such an instrument a couple of years ago and Googling around trying to find one with no success. The version pictured immediately above (and, I think, in Timothy’s photo) is this Chinese model imported by TFT Tools, but many other models are available.

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14 thoughts on “Dual-reading calipers with Imperial/SI units on same dial

  1. I’ve been using one of these for years and think that it is great. The only time that I had trouble was when I dropped it once and the gears skipped a few teeth inside. It didn’t break but it didn’t go to zero at the end anymore. After a bunch of fiddling around with sliding it apart and turning the gear a bit, I gave up and just popped off the needles and manually reset it that way. I think that if this one ever breaks in a permanent way I’ll get a good digital one. The way that they are built, they don’t have gears to skip.

    Beware of the cheap digital calipers. They seem to work fine but chew through batteries rather quickly.

  2. I, too, have had one for several years. It’s handy for measuring parts of unknown origin (“Is this shaft 1/4” or 6mm?).
    I also had the gear skip a tooth. On a normal dial caliper, that’s not a big deal, you just rotate the dial to zero the pointer. Well, this has two pointers, so they no longer both zero at the same place.
    Finally, the metric scale is 2mm/rotation, so you have to be extra careful of reading measurements.

  3. Those would be very handy. Although after such a long time at not having something like that I find I can convert from metric into imperial reasonably well now (how many thou in a mm again?). I find I prefer the analogue ones. Sometimes I want to take a smidge off something when machining and don’t bother using the scale on the lathe but I get a good feel for how much a smidge is by how far the needle on the calipers moves.

    I have also dropped mine and had them skip but I was able to take them apart and reset them.

  4. I must be misunderstanding, because the way I’m imagining this is completely insane.

    Why not just have one needle and print two separate scales on the dial? What important detail have I missed that makes it worthwhile to have all that complicated clockworks in there for this dual-needle system?

    1. I think because the two scales aren’t related. You want a caliper pointer to have one revolution of the dial match some multiple of the measurements on the linear scale. The dial is showing you the fraction between the linear marks on the sliding scale. This caliper has two linear scales which aren’t multiples of each other. So you need two needles to show the two different fractions.

      I did have to think about that a bit so it’s not a silly question. I don’t think my explanation is the clearest but hopefully you understand what I mean!

      1. Oh, Of course. I understand now.

        I was imagining a digital caliper where the absolute measurement is displayed on the dial. Here only the FRACTION is displayed on the dial.

        Thanks.

  5. Re: how long they’ve been available, I’ve had mine for almost 8 years. There’s no technical reason they couldn’t have been made a few hundred years ago, and the conflict that required its invention — metric vs. imperial units — started before I was born.

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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