7 ms·

I use it whenever I have something mildly annoying to convert, especially dates. e.g. https://www.wolframalpha.com/input/?i=1636221900+unix+time+in+warsaw https

by pxx 5y ago

I use it whenever I have something mildly annoying to convert, especially dates. e.g. https://www.wolframalpha.com/input/?i=1636221900+unix+time+in+warsaw https://www.wolframalpha.com/input/?i=1636221900+unix+time+i... Probably an incredibly trivial use-case but still useful regularly for me...

neltnerb 5y ago
It doesn't work so good for times but I often use Google search to multiply numbers with units together and get a result in the units I want without having to worry about screwing up unit conversions. Example: 4 atomic mass units * (1000 nm/sec)^2 Google Result: 6.64215616 × 10-39 joules I use this all the time. I use wolfram alpha for solving equations or systems of equations but I use google for unit conversions because it's got better input parsing (frankly). I should try the wolfram alpha math entry mode probably, I think that didn't exist when I started using it. If I could manually enter the equations with stricter formatting to ensure it's interpreted properly I'd use it more.
- mananaysiempre 5y ago
  A reminder that GNU Units still exists, e.g. $ units Currency exchange rates from FloatRates (USD base) on 2021-01-17 3677 units, 109 prefixes, 114 nonlinear units You have: 4 amu * (1000 nm/s)^2 You want: joules * 6.6421563e-39 / 1.5055352e+38 You have: ^D It’s slightly less DWIMish (you have to say “atomicmassunits”, “atomicmassunit”, “amu”, or “u”, not “atomic mass units”) and somewhat awkward as a separate tool, but then resorting to your web browser for unit conversions is awkward in a different way. Non-interactive invocations, like units VALUE-OR-UNIT UNIT, work as well. [1]: https://www.gnu.org/software/units/ https://www.gnu.org/software/units/
  - BenjiWiebe 5y ago
    +1 for 'units'. I like it for conversion between millilightseconds and miles, to get the theoretical best-case latency between two places. i.e. if it's x milliseconds ping, it can't be more than m miles away.
    - pxx 5y ago
      You have a missing factor of two.
      - deleted 5y ago
        [deleted]
  - neltnerb 5y ago
    Thanks for the reminder =) Alas, I often have to do these kinds of calculations on a random publicish computer or my phone and Google's converter is platform-independent. But not using Google services when feasible is certainly net good. And of course my TI-89 had equally good unit conversion for practical purposes (since you can define your own units) so somehow the world is still playing catchup to a calculator from the 90s...
    - mananaysiempre 5y ago
      If you’re organized enough to have space for Termux on your phone, it does wonders in this department. I feel silly every time I punch Python code into that teensy touch keyboard, but damned if I know anything else that has a better input UI and isn’t orders of magnitude less versatile. (Maple Calculator and microMathematics are still on the “there was an attempt” level, in my experience.)
    - acjohnson55 5y ago
      The TI-89 was/is an amazing device.
    - kragen 5y ago
      There's an Android GUI for a units(1) calculator in F-Droid. I have it on my phone.
- mananaysiempre 5y ago
  ... Seriously, though, if you’re actually need this type of calculation regularly and didn’t just pick a random example, atomic-scale calculations are absolutely miserable to do in SI (and this is not a problem, it’s a human-scale, engineering system, after all; and its metrological aspects, which were the actual advance originally, are completely unimportant here). If I had to do this in my head or with a desk calculator, I’d just do it in high-energy units (c = ℏ = 1, mass and energy in eV, length and time in eV^-1). So, 4 amu = 4 × 0.93 GeV (a proton weighs 939 MeV, an amu is slightly smaller due do binding energy, rounding to 1 GeV is good enough for most purposes) ≈ 4 GeV, (1000 nm / s)^2 = (1e4 Å / s)^2 = (1e4 / 1.97 keV^-1 s^-1)^2 (an angstrom is a typical atomic size, a keV is a typical [large] atomic energy, a fermi aka femtometer is a typical nuclear size, a MeV is a typical [not so large] nuclear energy, remember any of 197 MeV fm = 1.97 keV Å = 1, though again 200 is almost always good enough) ≈ (1e4 / 2 keV^-1 s^-1)^2 = 25e6 keV^-2 s^-2, 4 GeV × 25e6 keV^-2 s^-2 = 4e6 keV × 100e6/4 × keV^-2 s^-2 = 1e14 keV^-1 s^-2. This is slightly inconvenient, we wanted energy in eV, but the seconds don’t seem to want to go away. I don’t remember Planck’s constant in eV s, but I do remember 2 keV Å ≈ 1 and 300e3 km/s = 3e8 m/s = 1, so let’s sprinkle it with those, 1e14 keV^-1 s^-2 ≈ 1e14 keV^-1 s^-2 × (2 keV Å)^2 / (3e8 m/s)^2 = 4/9 × 1e14 × 1e-16 keV Å^2 m^-2 = 0.44 × 1e14 × 1e-16 keV × (1e-10)^2 ≈ 0.44e-22 keV ≈ 0.44e-19 eV. The hardest part is pretending to be a normal person: you have to remember what an electronvolt actually is in normal units. Good thing this is numerically the same as remembering the charge of an electron in coulombs (1 eV = 1.6e-19 J), 0.44e-19 eV = 0.44e-19 eV × 1.6e-19 J / eV (turns out converting to a decimal fraction wasn’t a good idea after all, powers of two FTW) ≈ 4/9 × 16 × 1e-1 × 1e-19 × 1e-19 J = 64/9 × 1e-39 J ≈ 63/9 × 1e-39 J = 7e-39 J. Good enough to a couple percent. OK, I won’t pretend that this is easy or that I did it flawlessly the first time just now, but I do think this looks like a skill you could plausibly learn, unlike the textbook “SI all the things” calculation. The good news is that you’ve just seen essentially all the relevant constants you’re going to have to remember, except maybe Avogadro’s number if you’re going to have moles somewhere. (One place where this doesn’t help is first-principles chemistry, things like electrolysis, because you need to subtract large binding energies to get a change that’s hundreds to thousands times smaller. Calculating things to a couple percent just isn’t good enough.)
  - neltnerb 5y ago
kragen 5y ago
I use GNU date(1) for this: $ TZ=Europe/Warsaw date --date=@1636221900 sáb 06 nov 2021 19:05:00 CET $ TZ=Europe/Warsaw date --date=2021-11-06T19:05 +%s 1636221900 $ echo $(( ($(TZ=Europe/Riga date +%s --date=2021-11-05T17:00) - $(TZ=America/New_York date +%s --date=2021-12-05T09:00)) / 3600 )) -719 However, this is super dangerous, because for whatever reason date(1) lies if you give it a nonexistent timezone, pretending that it understands you but actually giving you UTC: $ TZ=Mars date --date=@1636221900 sáb 06 nov 2021 18:05:00 Mars There's a list of valid timezones that you can conveniently browse with tab-completion after you spend 14 keystrokes to navigate there: $ TZ=/usr/share/zoneinfo/Europe/ Amsterdam Berlin Chisinau Isle_of_Man Lisbon Mariehamn Paris San_Marino Stockholm Vaduz Zagreb Andorra Bratislava Copenhagen Istanbul Ljubljana Minsk Podgorica Sarajevo Tallinn Vatican Zaporozhye Astrakhan Brussels Dublin Jersey London Monaco Prague Saratov Tirane Vienna Zurich Athens Bucharest Gibraltar Kaliningrad Luxembourg Moscow Riga Simferopol Tiraspol Vilnius Belfast Budapest Guernsey Kiev Madrid Nicosia Rome Skopje Ulyanovsk Volgograd Belgrade Busingen Helsinki Kirov Malta Oslo Samara Sofia Uzhgorod Warsaw $ TZ=/usr/share/zoneinfo/Europe/Riga date dom 07 nov 2021 06:50:44 EET I wish I had a really good calendar math utility program that handled this sort of thing properly.
- abecedarius 5y ago
  > I wish I had a really good calendar math utility Might be a good learning exercise in machine learning: translating natural-language queries from that domain to whatever standard utility.
  - kragen 5y ago
    Maybe, and it wouldn't have to be as slow and unresponsive as Wolfram Vertical Line Alpha or obscure your answers as an attempt to upsell you, but I think it would still tend to have the same kinds of essential usability problems: a gulf of execution in figuring out how to phrase a query so the system would understand it, and a gulf of evaluation in figuring out whether the calculation it had carried out was the calculation you wanted.

by pxx 5y ago

neltnerb 5y ago

It doesn't work so good for times but I often use Google search to multiply numbers with units together and get a result in the units I want without having to worry about screwing up unit conversions. Example: 4 atomic mass units * (1000 nm/sec)^2 Google Result: 6.64215616 × 10-39 joules I use this all the time. I use wolfram alpha for solving equations or systems of equations but I use google for unit conversions because it's got better input parsing (frankly). I should try the wolfram alpha math entry mode probably, I think that didn't exist when I started using it. If I could manually enter the equations with stricter formatting to ensure it's interpreted properly I'd use it more.

mananaysiempre 5y ago
A reminder that GNU Units still exists, e.g. $ units Currency exchange rates from FloatRates (USD base) on 2021-01-17 3677 units, 109 prefixes, 114 nonlinear units You have: 4 amu * (1000 nm/s)^2 You want: joules * 6.6421563e-39 / 1.5055352e+38 You have: ^D It’s slightly less DWIMish (you have to say “atomicmassunits”, “atomicmassunit”, “amu”, or “u”, not “atomic mass units”) and somewhat awkward as a separate tool, but then resorting to your web browser for unit conversions is awkward in a different way. Non-interactive invocations, like units VALUE-OR-UNIT UNIT, work as well. [1]: https://www.gnu.org/software/units/ https://www.gnu.org/software/units/
- BenjiWiebe 5y ago
  +1 for 'units'. I like it for conversion between millilightseconds and miles, to get the theoretical best-case latency between two places. i.e. if it's x milliseconds ping, it can't be more than m miles away.
  - pxx 5y ago
    You have a missing factor of two.
    - deleted 5y ago
      [deleted]
- neltnerb 5y ago
  Thanks for the reminder =) Alas, I often have to do these kinds of calculations on a random publicish computer or my phone and Google's converter is platform-independent. But not using Google services when feasible is certainly net good. And of course my TI-89 had equally good unit conversion for practical purposes (since you can define your own units) so somehow the world is still playing catchup to a calculator from the 90s...
  - mananaysiempre 5y ago
    If you’re organized enough to have space for Termux on your phone, it does wonders in this department. I feel silly every time I punch Python code into that teensy touch keyboard, but damned if I know anything else that has a better input UI and isn’t orders of magnitude less versatile. (Maple Calculator and microMathematics are still on the “there was an attempt” level, in my experience.)
  - acjohnson55 5y ago
    The TI-89 was/is an amazing device.
  - kragen 5y ago
    There's an Android GUI for a units(1) calculator in F-Droid. I have it on my phone.
mananaysiempre 5y ago
... Seriously, though, if you’re actually need this type of calculation regularly and didn’t just pick a random example, atomic-scale calculations are absolutely miserable to do in SI (and this is not a problem, it’s a human-scale, engineering system, after all; and its metrological aspects, which were the actual advance originally, are completely unimportant here). If I had to do this in my head or with a desk calculator, I’d just do it in high-energy units (c = ℏ = 1, mass and energy in eV, length and time in eV^-1). So, 4 amu = 4 × 0.93 GeV (a proton weighs 939 MeV, an amu is slightly smaller due do binding energy, rounding to 1 GeV is good enough for most purposes) ≈ 4 GeV, (1000 nm / s)^2 = (1e4 Å / s)^2 = (1e4 / 1.97 keV^-1 s^-1)^2 (an angstrom is a typical atomic size, a keV is a typical [large] atomic energy, a fermi aka femtometer is a typical nuclear size, a MeV is a typical [not so large] nuclear energy, remember any of 197 MeV fm = 1.97 keV Å = 1, though again 200 is almost always good enough) ≈ (1e4 / 2 keV^-1 s^-1)^2 = 25e6 keV^-2 s^-2, 4 GeV × 25e6 keV^-2 s^-2 = 4e6 keV × 100e6/4 × keV^-2 s^-2 = 1e14 keV^-1 s^-2. This is slightly inconvenient, we wanted energy in eV, but the seconds don’t seem to want to go away. I don’t remember Planck’s constant in eV s, but I do remember 2 keV Å ≈ 1 and 300e3 km/s = 3e8 m/s = 1, so let’s sprinkle it with those, 1e14 keV^-1 s^-2 ≈ 1e14 keV^-1 s^-2 × (2 keV Å)^2 / (3e8 m/s)^2 = 4/9 × 1e14 × 1e-16 keV Å^2 m^-2 = 0.44 × 1e14 × 1e-16 keV × (1e-10)^2 ≈ 0.44e-22 keV ≈ 0.44e-19 eV. The hardest part is pretending to be a normal person: you have to remember what an electronvolt actually is in normal units. Good thing this is numerically the same as remembering the charge of an electron in coulombs (1 eV = 1.6e-19 J), 0.44e-19 eV = 0.44e-19 eV × 1.6e-19 J / eV (turns out converting to a decimal fraction wasn’t a good idea after all, powers of two FTW) ≈ 4/9 × 16 × 1e-1 × 1e-19 × 1e-19 J = 64/9 × 1e-39 J ≈ 63/9 × 1e-39 J = 7e-39 J. Good enough to a couple percent. OK, I won’t pretend that this is easy or that I did it flawlessly the first time just now, but I do think this looks like a skill you could plausibly learn, unlike the textbook “SI all the things” calculation. The good news is that you’ve just seen essentially all the relevant constants you’re going to have to remember, except maybe Avogadro’s number if you’re going to have moles somewhere. (One place where this doesn’t help is first-principles chemistry, things like electrolysis, because you need to subtract large binding energies to get a change that’s hundreds to thousands times smaller. Calculating things to a couple percent just isn’t good enough.)
- neltnerb 5y ago

kragen 5y ago

I use GNU date(1) for this: $ TZ=Europe/Warsaw date --date=@1636221900 sáb 06 nov 2021 19:05:00 CET $ TZ=Europe/Warsaw date --date=2021-11-06T19:05 +%s 1636221900 $ echo $(( ($(TZ=Europe/Riga date +%s --date=2021-11-05T17:00) - $(TZ=America/New_York date +%s --date=2021-12-05T09:00)) / 3600 )) -719 However, this is super dangerous, because for whatever reason date(1) lies if you give it a nonexistent timezone, pretending that it understands you but actually giving you UTC: $ TZ=Mars date --date=@1636221900 sáb 06 nov 2021 18:05:00 Mars There's a list of valid timezones that you can conveniently browse with tab-completion after you spend 14 keystrokes to navigate there: $ TZ=/usr/share/zoneinfo/Europe/ Amsterdam Berlin Chisinau Isle_of_Man Lisbon Mariehamn Paris San_Marino Stockholm Vaduz Zagreb Andorra Bratislava Copenhagen Istanbul Ljubljana Minsk Podgorica Sarajevo Tallinn Vatican Zaporozhye Astrakhan Brussels Dublin Jersey London Monaco Prague Saratov Tirane Vienna Zurich Athens Bucharest Gibraltar Kaliningrad Luxembourg Moscow Riga Simferopol Tiraspol Vilnius Belfast Budapest Guernsey Kiev Madrid Nicosia Rome Skopje Ulyanovsk Volgograd Belgrade Busingen Helsinki Kirov Malta Oslo Samara Sofia Uzhgorod Warsaw $ TZ=/usr/share/zoneinfo/Europe/Riga date dom 07 nov 2021 06:50:44 EET I wish I had a really good calendar math utility program that handled this sort of thing properly.

abecedarius 5y ago
> I wish I had a really good calendar math utility Might be a good learning exercise in machine learning: translating natural-language queries from that domain to whatever standard utility.
- kragen 5y ago
  Maybe, and it wouldn't have to be as slow and unresponsive as Wolfram Vertical Line Alpha or obscure your answers as an attempt to upsell you, but I think it would still tend to have the same kinds of essential usability problems: a gulf of execution in figuring out how to phrase a query so the system would understand it, and a gulf of evaluation in figuring out whether the calculation it had carried out was the calculation you wanted.