• alcoholicorn [comrade/them, doe/deer]
    ·
    4 years ago

    Quick, without a calculator and without paper tell me how many feet are in two miles

    Quick, without a calculator tell me, if you have a 1m plank and cut it into half, then cut one half into thirds, and tell me how long each piece is.

    In metric that's (1m-.125)/2, which a calculator tells me is 499.9375. Chop that into thirds and a calculator tells me it's 166.5625

    In imperial (40"-1/8")/2 is 19 and 15/16", chopping that into thirds, 19 and 15/16"-3/8"= 19 and 9/16", and divide by 3 and you get 6 and 25/48".

    No messy decimals, no loss of precision.

    Another problem with feet and inches is that there isnt anything smaller than them

    Fractions, and if you need something smaller than 1/256, there's thou.

    • ToastGhost [he/him]
      ·
      4 years ago

      Youre still allowed to divide up a meter into fractions if it makes your math easier, my point with inches and fractions was that there is no way to describe something smaller than an inch with a simple integer number, there are no nano-inches, and if there were, they would probably be a new entirely arbitrary fraction of an inch.

      • alcoholicorn [comrade/them, doe/deer]
        ·
        4 years ago

        Youre still allowed to divide up a meter into fractions if it makes your math easier, my point with inches and fractions was

        I mean technically true, but I get the sense metric users aren't trained to use fractions. Do European carpenters use fractions, or fuck around with 7 significant figures?

      • thisismyrealname [he/him]
        ·
        4 years ago

        i mean north american machinists use thousands of an inch or (0.001") which is in the same realm as a micrometer

    • triangle [none/use name]
      ·
      edit-2
      4 years ago

      1/2 = 0.5 1/3 = 0.333... just multiply them together. Pick as much or as little accuracy as you want, 5 x 33 / 10 gives you about how many cm you need. If you need a tighter tolerance, 5 x 333 / 10 is how many mm you need.

      Silly Americans would have to learn how to multiply in their heads and how to turn fractions into decimals, but otherwise they could divide lengths in their heads just like everyone else on the planet.

      • alcoholicorn [comrade/them, doe/deer]
        ·
        edit-2
        4 years ago

        A blade is usually 3.175 mm (1/8" in imperial), you can't subtract a multiple of that, then easily divide the result by 2 or 3 over and over without getting increasingly nasty decimals or losing precision.

        Cutting a 100 cm board in half isn't 100/2, it's (100-.3175)/2

        • triangle [none/use name]
          ·
          4 years ago

          If you need to actually divide a board into sixths just do like every other carpenter and mark off lines and cut to the right of the line and not on it exactly. Your last board is short, but they always are whether you marked it off in inches or cm. Take a look at a job sites garbage bin when they're framing, there are tons of ends of boards that routinely get tossed because they couldnt get it exactly right OR they shim the shit out of the last board, lol. They definitely dont divide the board into sixths perfectly including the fact that the width of the blade is going to shave off about 330 mm or about an 1/8th inch

    • Segorinder [any]
      ·
      4 years ago

      Yes, the fractions are exact, but when you need to measure something, you probably won’t have anything marked for 48ths or whatever arbitrary fraction. You still have to make an approximation to use the closest fraction available.

      For the seven digit numbers you’re using, the loss of precision is less than one part in a million, which shouldn’t be an issue for cutting planks of wood.

      Also, there’s nothing about the metric system that stops you from using fractions.

      • 420sixtynine [any,comrade/them]
        ·
        4 years ago

        you probably won’t have anything marked for 48ths or whatever arbitrary fraction

        except the fractions aren't just random, that's the nice thing about it being divisible by 12, almost all of the time you do have those markers, so yes, you do have 48ths

        • Segorinder [any]
          ·
          4 years ago

          In this example we're talking about inches and an inch is not any more divisible by 12 than a centimeter. Generally you're not going to see 48 divisions crammed into an inch on a ruler. You can have a set of specialty yardsticks with divisions set up for dividing by 3, 5, 7 etc. but you could do that with a meter the same way.

          • 420sixtynine [any,comrade/them]
            ·
            edit-2
            4 years ago

            Except I have several tape measures with 64ths, they aren't exactly uncommon and you can do 48ths with 64ths

            • Segorinder [any]
              ·
              edit-2
              4 years ago

              The argument was that imperial was better because you could do an exact division and get 6 and 25/48".
              25 48ths is 33.333 repeating 64ths. You still have to eyeball a third of a division, the same way you would have had to eyeball half a millimeter.