• renzev@lemmy.world
    link
    fedilink
    English
    arrow-up
    17
    ·
    edit-2
    3 months ago

    I can’t tell which unit is more cursed: millihertz or meter hertz. Surely, anything that could be measured in millihertz is more natural to measure as a period, or as revolutions per minute or something, right?

    EDIT: Also, TIL about dpt. Thanks!

    A dioptre (British spelling) or diopter (American spelling), symbol dpt, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dpt = 1 m^−1.

    • Technus
      link
      fedilink
      arrow-up
      7
      ·
      3 months ago

      Something that occurs once a hour has a frequency of 277.777… μHz

    • Technus
      link
      fedilink
      arrow-up
      5
      ·
      3 months ago

      You know, I always figured optometry involved like, super complicated math and shit.

      Turns out it’s just basic arithmetic.

      Kinda like programming, in a way.

      • rockerface 🇺🇦@lemm.ee
        link
        fedilink
        arrow-up
        1
        ·
        3 months ago

        Yeah, from my experience ordering glasses, it’s mostly about making sure the lenses are aligned with my retinas to focus the light in the right spots. All the numbers are just a way to formalize those measurements so that the lens maker gets it right

        • Technus
          link
          fedilink
          arrow-up
          1
          ·
          3 months ago

          My last optometrist refused to tell me what my prescription was. I should have insisted, they’ve since closed up shop.

    • bleistift2@sopuli.xyz
      link
      fedilink
      English
      arrow-up
      3
      ·
      edit-2
      3 months ago

      TIL about dpt

      Tell me you don’t [Edit: need] glasses without telling me you don’t need glasses :D

      • renzev@lemmy.world
        link
        fedilink
        English
        arrow-up
        2
        ·
        3 months ago

        I actually do have glasses, I just never bothered learning about any of the technical details behind my lenses. Optometrist measured my eyes, I chose the cheapest frame the store offered, came back a week later to pick up the glasses and that’s about it.

    • Eheran@lemmy.world
      link
      fedilink
      arrow-up
      3
      ·
      3 months ago

      Speed as meter per hertz is a rather odd case, like with a machine that goes in discrete steps.

      In any case, I never use implied multiplication (and others) and always simply put everything where it should be.

      • Skua@kbin.earth
        link
        fedilink
        arrow-up
        6
        ·
        3 months ago

        Speed is metre hertz rather than metre per hertz. Metres per hertz would measure absement, which is a measure of how far away something is from a start point and for how long. So being twice as far away for half the time would be the same amount of absement.

        • Eheran@lemmy.world
          link
          fedilink
          arrow-up
          2
          ·
          3 months ago

          Yes, sorry for the little error, my point is that m*Hz it is not generally speed but only in specific cases. Hz is not just “per time” but “something occurring x times per time”, like a frequency or revolutions. You can not use it for regular speed, it has to be a periodic event. That is how it is defined:

          The hertz is defined as one per second for periodic events.

          This is why we have Becquerels to count decay events, which are random and not periodic, but the unit is also 1/s. And for the same reason you can not use m*Bq as speed.

          • bleistift2@sopuli.xyz
            link
            fedilink
            English
            arrow-up
            2
            ·
            3 months ago

            I never knew that Hertz requires a periodic event. Thanks for that and the Becquerel explanation!