3 ms·

> milliangstroms There is a perfectly sensible nearby SI unit called the picometre (pm). 10 mÅ = 1 pm. https://en.wikipedia.org/wiki/Picometre https://en.wikip

• gilleain 4y ago
  Yes, while the ångström is often used for bond lengths, I've only heard of picometers used for smaller lengths.
• fritzo 4y ago
  ok but 'milliangstroms' immediately conveys a sense of relative error
• swamp40 4y ago
  Same as "mils" for thousands of an inch. It's actually wildly popular in the US.
  • nayuki 4y ago
    Mils are a terrible compromise. On the one hand, they acknowledge that dividing by 1000 is useful and that it's easier to work on a linear scale instead of mixed units and fractions. On the other hand, it stubbornly clings onto the inch instead of embracing the millimetre or micrometre. As a side note, I heard of carpenters who work in decimal feet. Yeah, that's great, adding yet another option to the mix. Everyone else talks in feet and inches.
• marcosdumay 4y ago
  When every measure around is on the same unity, you use that as your base unity. If you are designing a large steel piece for milling, you will write a length of 1000mm, not 1m.
  • kennywinker 4y ago
    1m and 1000mm are not the same length. 1000mm and 1.000m are the same length.
    • brokensegue 4y ago
      Not according to https://en.m.wikipedia.org/wiki/Significant_figures https://en.m.wikipedia.org/wiki/Significant_figures
      • foxyv 4y ago
        Pretty close. If they added an additional zero to make 1.0000 meters they would be the same number of significant figures technically. But it's all convention. I've been in classes where 1.000 would be 4 significant figures. > 120.0000 consists of six significant figures (1, 2, and the four subsequent zeroes) except for the last zero If the resolution is to 0.001.
        • tomjakubowski 4y ago
          1.000 has 4 significant figures. Absent other context, 1000 has 1.
          • foxyv 4y ago
            When arguing convention, everyone is right, and everyone is wrong.
      • kennywinker 4y ago
        You're right that I'm remembering my sig-fig rules wrong, but you're not entirely right: > Zeros to the right of the last non-zero digit (trailing zeros) in a number with the decimal point are significant if they are within the measurement or reporting resolution. > 1.200 has four significant figures (1, 2, 0, and 0) if they are allowed by the measurement resolution. and > Trailing zeros in an integer may or may not be significant, depending on the measurement or reporting resolution. So my first example "1m and 1000mm" actually might be the same length, depending on if those zeros are significant or not which has not been clearly communicated. My second example "1000mm and 1.000m" is also ambiguous, since 1.000m is clear(ish) about its sig-figs, while 1000mm is not. I suppose I could have written "1000. mm" Best solution imo would probably be: - something that actually specified the error: 1m ± 0.0001m - or using words to indicate what's meant: "exactly 1000mm"
• kwoff 4y ago
  The wikipedia article https://en.wikipedia.org/wiki/Angstrom https://en.wikipedia.org/wiki/Angstrom has some historical context: 'In the late 19th century, spectroscopists adopted 10^−10 of a metre as a convenient unit (...). However, they soon realized that the definition of the metre at the time, based on a material artifact, was not accurate enough for their work. So, around 1907 they defined their own unit of length, which they called "Ångström", based on the wavelength of a specific spectral line. It was only in 1960, when the metre was redefined in the same way, that the angstrom became again equal to 10^−10 meter.'