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| A warning to engineers about calculators |
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| Russ_A:
I decided to try a calculator app called Hiper Calc for Android. If you search for calculator app reviews it'll be there, highly recommended. At first I was very impressed by its ability to create user layouts. Really cool stuff. But within only a single day I uncovered several critical calculation flaws. For example, it has options for precision which are confusing. They seemed to be based on what size screen you were using. It turns out that whatever number of digits you choose to display, often 6 for readablity, is what the calculator would actually use in its calculations, which includes the ANS function (previous calculation result), stored values, etc. Crazy. So by making it a bit more readable on your phone you might only be using 4 or 5 digits in your calculations. And then I was testing its random number generator and it was completely flawed. It uses the same random number for all instances in a calculation, but then sometimes it doesn't, seemingly at random. And the last one I found was with its use of %. When typing an expression it'll put brackets around the number when you type in %, so you type 9 - 10 % and it'll have 9 - (10)% for the expression on the display. Seems great, right? What a good way to clarify what's going on. Wrong. That evaluates to 8.1. No kidding. I've been in contact with the developer and they're claiming that's the correct way of doing percentages. They just have no idea what they're doing. I explained that % should always be the same as /100 but they don't believe me. Note that this calculator allows full symbology and the entire expression to be entered at once before evaluating. This isn't some old school stepwise input. Anyway, my point is that in only a single day I've uncovered serious flaws with one of the seemingly best Android calculators out there. Please don't use a calculator that hasn't been through rigorous quality testing to do engineering calculations. I can imagine even a doctor or nurse screwing up a dosage because of the % flaw. It's crazy. So despite how cool that app is I guess I'll stick to using a handheld one that's been through the rigors of proper quality control and testing. As someone who does calculations for a living this has really put me off using apps. |
| jpanhalt:
What happens when you try (9 - 10)% or 9% -10%? Frankly, I rarely calculate with percent, and it's not completely clear what answer you wanted for 9 - 10% or 9- (10)%. |
| Squarewave:
That calculators days are numbered. |
| Russ_A:
My problem with it is that it's an amazing calculator. It let's you make your own layouts with the functions you want. It's damn-near perfect that way, which is why it's so popular. But being able to find such critical flaws in it in only a day is ridiculous. I'm sure I can find more. And the developer doesn't know what they're doing as far as calculations are concerned. The precision flaw is simply inexcusable. The percent calculation error, and their refusal to acknowledge it is crazy too. I never realized the risks of a dodgy app until today. It could cost someone serious money or make a serious mistake that could cause real harm. I now understand why there are calculator test suites. This obviously wouldn't come anywhere close to passing. I have two Casio fx-991EX calculators, one for home and one for work. I thought I could finally just use my phone because I found an app I loved. At least I know I can trust the Casio when I type a percent sign, and I know that it's storing fifteen or so digits in memory, not 4. Thank god the only thing the app might have thrown off for me is a drafting calculation or a voltage drop. I don't design bridges or medical devices. |
| golden_labels:
For the percent function the result is correct: 9 -10% = 9 - (9 * 10/100) = 9 - 0.9 = 8.1. I don’t recall it ever working otherwise. I also don’t see how it would work, given pocket, PoS, and office calculators do tail operations only. However, the warning holds in general. Given you emphasized the part about reviews: beyond calculators. Don’t trust those review systems. If anything, read only negative reviews and consider them only after carefully reading and evaluating. Even if the reviews were honest, and often they are not, the entire system can’t work. Consider, who posts those opinions. Those are completely random, anonymous people, under no obligation to express anything beyond their first emotional impression, in overwhelming majority lacking expertise to provide a reliable opinion and more often not having basic skills to conduct a test, and with the comment window too short to allow for a proper test anyway. I’ll also skip the entire topic of who runs those review systems. If you want an opinion, there is a lot of people doing honest, proper reviews. Dave is one of them. You know, who gives the opinion. You can judge their abilities, their knowledge and experience. You know their testing methods. Even somewhat entertainment(1) YouTube channels, like Project Farm, are worth orders more than any random opinions system. (1) I do respect the channel and that comment isn’t meant to belittle it. He does a great job. But some limitations, like being able to afford only a single specimen being tested, hamper the strength of the results. Some tests are also humorous and I believe this is intentional. Nothing wrong with that as long as one keeps that in mind. To be honest it would be detrimental to Project Farm, if tests were proper: it would then become a horrible, boring job. |
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