7 ms·

How does the calculator percent key work? (2008)

128 points by vmarsy 12y ago

evolve2k 12y ago
So I worked for over 10 years as an Accountant/CPA and over 6 years as a coder and all this time I've never know how to use that damn key. Thanks!
stevecalifornia 12y ago
I wish I had known this 20 years ago. Something so simple and so useful.
- thaumasiotes 12y ago
  Is it really more simple to type "72 + 5 %" than to type "72 * 1.05"?
  - copperx 11y ago
    It is. It saves you from an extra mental operation. What's the price of that $56 shirt after 22% off? Doing 1-22/100 in your head adds an extra possibility for error.
    - pluma 11y ago
      1 - 0.22 * 56 Using a classic calculator (i.e. one that doesn't obey operator precedence and thus doesn't need parentheses) that's three operators (including "equals") and a total of 10 buttons to press. 56 - 22% That's 6 buttons to press. Arguably, 6 is less than 10 [citation needed]. But I find it doubtful that this saves a noticeable amount of effort. If you're multiplying by decimals, you already read "22%" as "0.22" and "-22%" as "(1 - 0.22)". There's no mental overhead in typing that unless you mean rote copying. Maybe this is a matter of school system priorities. In my country children are introduced to percentages using cross-multiplication. They are also required to write the entire calculation process down in exams in order to pass (to make sure you actually understand the calculation and aren't just blindly entering numbers into a calculator).
  - bitwize 11y ago
    If you don't know math, then yes. Most people don't know or care that "adding 5% tax" is equivalent to multiplying by 1.05. They just know that you have to add 5% for tax. So 72 + 5% makes perfect sense; 72 * 1.05 is terribly confusing.
    - DanBC 11y ago
      But that's why most people get stuck with percentages, even if you give them a calculator. They can work out what 8% of 347 is. But ask them what 43 is as a percentage of 172 and they can't do it. Or if a widget costs £250 after a 20% discount, how much did it cost before -- they can't do it.
      - pluma 11y ago
        This actually puts these people at a disadvantage in real life. Just look at the arbitrary packaging sizes and how effective they are at fooling people into thinking they're cheaper or equally expensive just because they're unable to figure out that the "new packaging with 25% extra for free" is actually more expensive than the old packaging that contained a little bit less.
        userbinator 11y ago
        There's regulations that mandate unit price information: http://en.wikipedia.org/wiki/Unit_price_information_in_supermarkets http://en.wikipedia.org/wiki/Unit_price_information_in_super... ...but even that information is usually printed in a smaller font and can be misleading: http://talkingcents.consumercredit.com/2011/02/23/unit-pricing-and-a-dirty-little-secret/ http://talkingcents.consumercredit.com/2011/02/23/unit-prici... It gives a whole deeper meaning to that classic Barbie utterance: "Maths is hard. Let's go shopping!"
    - learnstats2 11y ago
      Anything beyond the most simple calculation is obfuscated by the % button. As an example: Reverse an erroneous 10% discount. Use the % button?
  - copperx 11y ago
    It is. It saves you from an extra mental operation. What's the price of that $56 shirt after 22% off? Doing 1-22/100 in your head adds an extra possibility for error.
kleer001 12y ago
Whoa, that's a lot more complicated than I give calculators for being.
jtbarrett 12y ago
If you're tying to follow along in calc.exe but the percent key is disabled, switch to Standard mode. It's not on in the other modes.
- joshschreuder 11y ago
  Oddly enough, on Windows 8 it appears in Scientific and Programmer modes but is greyed out, and I couldn't get it to activate. Why not hide it?
  - agarcia-deniz 11y ago
    just noticed that myself, had pretty much the same thought.
  - userbinator 11y ago
    ...or why not make it usable in all modes? I think the calculator in Windows 7 and above took a seriously backwards step in functionality - they seem to have thought that programmers don't need exponentiation nor square roots nor floating-point(!), so there is no such function in "programmer mode" and you cannot change the number base in "scientific mode". That would only be a minor annoyance, if not for the fact that switching between modes clears the accumulator! http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_programs/windows-7-calculator-not-useful/c61ef069-f5d6-422a-8973-7cff6fc36528 http://answers.microsoft.com/en-us/windows/forum/windows_7-w... It is a classic case of too much modality in UI design. The first time I discovered this "feature" after losing the result of a long calculation, I thought it was a bug or I'd accidentally hit the wrong key. When I found out this was by design, it elicited a loud enough "WTF!?" that caught my co-workers attentions and caused them to exclaim the same thing after showing it to them. Fortunately the calc.exe from XP runs fine on 7 and 8. There's another "feature" which I hadn't personally run into, but would be just as incensed if I did: https://social.technet.microsoft.com/Forums/windows/en-US/4ec1b55b-b516-471d-aa77-6b37b69d8df6/action?threadDisplayName=windows&forum=w7itproui https://social.technet.microsoft.com/Forums/windows/en-US/4e...
DonHopkins 12y ago
Dang, and I always thought it was to show the percentage of battery power left.
- vt240 11y ago
  That is fantastic, something I never would have thought of!
nextos 12y ago
> The Windows calculator percent sign works the same way as those cheap pocket calculators I never understood how these cheap calculators worked. I'm glad most serious desktop calculator apps, like the OS X one, have a RPN mode. As a high schooler, my dad forced me to switch to RPN calculators when we began doing very lengthy calculations. People thought I was a freak. But in retrospect, it was an awesome decision. With a stack, things are much simpler. You don't need those clumsy memory registers or parentheses, and all operators have a very simple semantics. As a bonus point, an innocent looking HP15C implements or can implement quite advanced numerical methods. It was a secret retro weapon from the 80s when all they allowed were non-graphical calculators.
- lambdaelite 12y ago
  After years of using an HP, I am literally unable to use anything but RPN without significant conscious thought. I'm faster with pencil and paper (or an abacus!) than using a non-RPN calculator at this point.
- mintplant 12y ago
  Any recommendations for a good RPN calculator on Linux?
  - tokenrove 12y ago
    M-x calc in emacs
  - lambda 12y ago
    I generally just use dc on the command line. Pretty bare bones, but gets the job done. M-x calc in Emacs is a very full-featured RPN calculator. On Android, I use Droid48, a great HP48 emulator: https://play.google.com/store/apps/details?id=org.ab.x48 https://play.google.com/store/apps/details?id=org.ab.x48 ; I also have RealCalc (https://play.google.com/store/apps/details?id=uk.co.nickfines.RealCalc https://play.google.com/store/apps/details?id=uk.co.nickfine...) installed, which I figured I'd use more due to the bigger buttons by default, but I still reach for Droid48 most often.
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WalterBright 12y ago
What a waste of a key. It's like those miserable cheat sheets for electronics that contain: V=IR R=V/I I=V/R First off, if you don't know Ohm's Law you have no business doing anything with electronics - you're going to use the formulas wrongly. Secondly, if you can't trivially derive the various forms in your head, you have no business using them.
- deleted 12y ago
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cdcarter 12y ago
This makes me desperately miss my register tape 10-key at my old desk. I wish I could find an iPhone app that acts like a 10-key adding machine.
donatj 11y ago
I am honestly kind of shocked at the responses to this. We used it in school, I used it at home to figure out sales tax as a kid, I'm honestly shocked so many people don't know what the percent button on a calculator does.
- deleted 11y ago
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- JacobAldridge 11y ago
  Many HNers are just part of today's lucky 10,000. https://xkcd.com/1053/ https://xkcd.com/1053/
- deleted 11y ago
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- pluma 11y ago
  I had no idea because we learned to convert percentages before we were allowed to use calculators in school. So by the time we could have used the % button it was already second nature to read "x + 5%" as "x * 1.05".
- kokey 11y ago
  I used the % on the calculator as a kid a lot. Then for about 25 years I didn't touch a desktop calculator and was thinking in 75 x 1.05, so when I recently tried to use the percentage sign it didn't work intuitively for me. I tried 75 x 5% and that certainly gave me an answer that felt wrong.
- GFK_of_xmaspast 11y ago
  I thought hackers were famed for experimenting with hardware and interfaces and trying to ferret out all the secrets.
traditionals 11y ago
But I never wanted a button that worked like that. That's not what I care about when calculating percentages. I don't want an inlined relative percentile value, based on prior terms. I almost never need that, and thus never use the percentage key, because that makes it useless and the behavior is counter intuitive. What if I have a much longer chain of calculations to tally up? What I need, then, is a percentage for one of the terms in isolation, BEFORE I start calculating. If I have an arbitrarily large number, and an arbitrarily complex percentile value, which makes the percentile value difficult to determine in one's head, I want a button that performs as follows: 37.82726419 percent of 9999.928374666666 equals ??? Which gets keyed as: 37.82726419 % 9999.928374666666 = ??? Then, I take that number and roll it into any other subsequent equations. Too bad the button will never ever work that way, because "tradition."

128 points by vmarsy 12y ago

So I worked for over 10 years as an Accountant/CPA and over 6 years as a coder and all this time I've never know how to use that damn key. Thanks!

stevecalifornia 12y ago

I wish I had known this 20 years ago. Something so simple and so useful.

thaumasiotes 12y ago
Is it really more simple to type "72 + 5 %" than to type "72 * 1.05"?
- copperx 11y ago
  It is. It saves you from an extra mental operation. What's the price of that $56 shirt after 22% off? Doing 1-22/100 in your head adds an extra possibility for error.
  - pluma 11y ago
    1 - 0.22 * 56 Using a classic calculator (i.e. one that doesn't obey operator precedence and thus doesn't need parentheses) that's three operators (including "equals") and a total of 10 buttons to press. 56 - 22% That's 6 buttons to press. Arguably, 6 is less than 10 [citation needed]. But I find it doubtful that this saves a noticeable amount of effort. If you're multiplying by decimals, you already read "22%" as "0.22" and "-22%" as "(1 - 0.22)". There's no mental overhead in typing that unless you mean rote copying. Maybe this is a matter of school system priorities. In my country children are introduced to percentages using cross-multiplication. They are also required to write the entire calculation process down in exams in order to pass (to make sure you actually understand the calculation and aren't just blindly entering numbers into a calculator).
- bitwize 11y ago
  If you don't know math, then yes. Most people don't know or care that "adding 5% tax" is equivalent to multiplying by 1.05. They just know that you have to add 5% for tax. So 72 + 5% makes perfect sense; 72 * 1.05 is terribly confusing.
  - DanBC 11y ago
    But that's why most people get stuck with percentages, even if you give them a calculator. They can work out what 8% of 347 is. But ask them what 43 is as a percentage of 172 and they can't do it. Or if a widget costs £250 after a 20% discount, how much did it cost before -- they can't do it.
    - pluma 11y ago
      This actually puts these people at a disadvantage in real life. Just look at the arbitrary packaging sizes and how effective they are at fooling people into thinking they're cheaper or equally expensive just because they're unable to figure out that the "new packaging with 25% extra for free" is actually more expensive than the old packaging that contained a little bit less.
      - userbinator 11y ago
        There's regulations that mandate unit price information: http://en.wikipedia.org/wiki/Unit_price_information_in_supermarkets http://en.wikipedia.org/wiki/Unit_price_information_in_super... ...but even that information is usually printed in a smaller font and can be misleading: http://talkingcents.consumercredit.com/2011/02/23/unit-pricing-and-a-dirty-little-secret/ http://talkingcents.consumercredit.com/2011/02/23/unit-prici... It gives a whole deeper meaning to that classic Barbie utterance: "Maths is hard. Let's go shopping!"
  - learnstats2 11y ago
    Anything beyond the most simple calculation is obfuscated by the % button. As an example: Reverse an erroneous 10% discount. Use the % button?
- copperx 11y ago
  It is. It saves you from an extra mental operation. What's the price of that $56 shirt after 22% off? Doing 1-22/100 in your head adds an extra possibility for error.

kleer001 12y ago

Whoa, that's a lot more complicated than I give calculators for being.

jtbarrett 12y ago

If you're tying to follow along in calc.exe but the percent key is disabled, switch to Standard mode. It's not on in the other modes.

joshschreuder 11y ago
Oddly enough, on Windows 8 it appears in Scientific and Programmer modes but is greyed out, and I couldn't get it to activate. Why not hide it?
- agarcia-deniz 11y ago
  just noticed that myself, had pretty much the same thought.
- userbinator 11y ago
  ...or why not make it usable in all modes? I think the calculator in Windows 7 and above took a seriously backwards step in functionality - they seem to have thought that programmers don't need exponentiation nor square roots nor floating-point(!), so there is no such function in "programmer mode" and you cannot change the number base in "scientific mode". That would only be a minor annoyance, if not for the fact that switching between modes clears the accumulator! http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_programs/windows-7-calculator-not-useful/c61ef069-f5d6-422a-8973-7cff6fc36528 http://answers.microsoft.com/en-us/windows/forum/windows_7-w... It is a classic case of too much modality in UI design. The first time I discovered this "feature" after losing the result of a long calculation, I thought it was a bug or I'd accidentally hit the wrong key. When I found out this was by design, it elicited a loud enough "WTF!?" that caught my co-workers attentions and caused them to exclaim the same thing after showing it to them. Fortunately the calc.exe from XP runs fine on 7 and 8. There's another "feature" which I hadn't personally run into, but would be just as incensed if I did: https://social.technet.microsoft.com/Forums/windows/en-US/4ec1b55b-b516-471d-aa77-6b37b69d8df6/action?threadDisplayName=windows&forum=w7itproui https://social.technet.microsoft.com/Forums/windows/en-US/4e...

DonHopkins 12y ago

Dang, and I always thought it was to show the percentage of battery power left.

vt240 11y ago
That is fantastic, something I never would have thought of!

nextos 12y ago

> The Windows calculator percent sign works the same way as those cheap pocket calculators I never understood how these cheap calculators worked. I'm glad most serious desktop calculator apps, like the OS X one, have a RPN mode. As a high schooler, my dad forced me to switch to RPN calculators when we began doing very lengthy calculations. People thought I was a freak. But in retrospect, it was an awesome decision. With a stack, things are much simpler. You don't need those clumsy memory registers or parentheses, and all operators have a very simple semantics. As a bonus point, an innocent looking HP15C implements or can implement quite advanced numerical methods. It was a secret retro weapon from the 80s when all they allowed were non-graphical calculators.

lambdaelite 12y ago
After years of using an HP, I am literally unable to use anything but RPN without significant conscious thought. I'm faster with pencil and paper (or an abacus!) than using a non-RPN calculator at this point.
mintplant 12y ago
Any recommendations for a good RPN calculator on Linux?
- tokenrove 12y ago
  M-x calc in emacs
- lambda 12y ago
  I generally just use dc on the command line. Pretty bare bones, but gets the job done. M-x calc in Emacs is a very full-featured RPN calculator. On Android, I use Droid48, a great HP48 emulator: https://play.google.com/store/apps/details?id=org.ab.x48 https://play.google.com/store/apps/details?id=org.ab.x48 ; I also have RealCalc (https://play.google.com/store/apps/details?id=uk.co.nickfines.RealCalc https://play.google.com/store/apps/details?id=uk.co.nickfine...) installed, which I figured I'd use more due to the bigger buttons by default, but I still reach for Droid48 most often.

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WalterBright 12y ago

What a waste of a key. It's like those miserable cheat sheets for electronics that contain: V=IR R=V/I I=V/R First off, if you don't know Ohm's Law you have no business doing anything with electronics - you're going to use the formulas wrongly. Secondly, if you can't trivially derive the various forms in your head, you have no business using them.

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cdcarter 12y ago

This makes me desperately miss my register tape 10-key at my old desk. I wish I could find an iPhone app that acts like a 10-key adding machine.

donatj 11y ago

I am honestly kind of shocked at the responses to this. We used it in school, I used it at home to figure out sales tax as a kid, I'm honestly shocked so many people don't know what the percent button on a calculator does.

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JacobAldridge 11y ago
Many HNers are just part of today's lucky 10,000. https://xkcd.com/1053/ https://xkcd.com/1053/
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pluma 11y ago
I had no idea because we learned to convert percentages before we were allowed to use calculators in school. So by the time we could have used the % button it was already second nature to read "x + 5%" as "x * 1.05".
kokey 11y ago
I used the % on the calculator as a kid a lot. Then for about 25 years I didn't touch a desktop calculator and was thinking in 75 x 1.05, so when I recently tried to use the percentage sign it didn't work intuitively for me. I tried 75 x 5% and that certainly gave me an answer that felt wrong.
GFK_of_xmaspast 11y ago
I thought hackers were famed for experimenting with hardware and interfaces and trying to ferret out all the secrets.

traditionals 11y ago

But I never wanted a button that worked like that. That's not what I care about when calculating percentages. I don't want an inlined relative percentile value, based on prior terms. I almost never need that, and thus never use the percentage key, because that makes it useless and the behavior is counter intuitive. What if I have a much longer chain of calculations to tally up? What I need, then, is a percentage for one of the terms in isolation, BEFORE I start calculating. If I have an arbitrarily large number, and an arbitrarily complex percentile value, which makes the percentile value difficult to determine in one's head, I want a button that performs as follows: 37.82726419 percent of 9999.928374666666 equals ??? Which gets keyed as: 37.82726419 % 9999.928374666666 = ??? Then, I take that number and roll it into any other subsequent equations. Too bad the button will never ever work that way, because "tradition."