This article says that NASA uses 15 digits after the decimal point, which I’m counting as 16 in total, since that’s how we count significant digits in scientific notation. If you round pi to 3, that’s one significant digit, and if you round it to 1, that’s zero digits.
I know that 22/7 is an extremely good approximation for pi, since it’s written with 3 digits, but is accurate to almost 4 digits. Another good one is √10, which is accurate to a little over 2 digits.
I’ve heard that ‘field engineers’ used to use these approximations to save time when doing math by hand. But what field, exactly? Can anyone give examples of fields that use fewer than 16 digits? In the spirit of something like xkcd: Purity, could you rank different sciences by how many digits of pi they require?
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I’m a waitress, and pie is $12.50.
Damn that’s pricey
Not if it’s a whole pie.
…
That is a whole pie, right?
Yes, but a small, 3-4 person one. Key lime though!
Worth it
baker. I measure pie based on how much I can fit in my mouth
I can’t say “professionally” but I learned CAD design with FreeCAD, and know the topological naming issue thoroughly.
Almost all “mystery” problems in CAD are due to a combination of the hacks that get around the Topological Naming Issue and π.
In CAD, you cookie, you brownie, you might even salad, but you stay the hell away from importing π as a reference on anything complex. For 3D printing, I never need better than 0.05mm so 3.1416.
Why would anyone use this fakenass number it makes no sense
I’m British, not American, so I use 7/22.
Rub it in, metric π, you imperialist rebel.
I’m a programmer and I remember 33 digits, but in practice I never use pi because I never have to deal with geometry
Retail, and to my knowledge among all my coworkers we have used zero digits of pi.
When I code in C++ I use 15 digits of pi after the decimal point (double float) but I have only rarely coded for money and have never used pi for those work products, so again, zero digits on the clock.
Ditto for restaurant work, although 2 decimal points would be more than enough if I needed the volume of a cake or other round food.
3.14159
Design of mechanical parts, specifically machined. 0.001" is a fairly tight tolerance for my applications, 0.0001" is going to cost a pretty penny and is used judiciously. We don’t really need to go to 3.14159 but I honestly think we do because it rhymes.
That is 0.025 Millimeter in normal units
You can say 25 micrometers
Yes, it’s technically correct (which we all know is the best kind of correct) and engineers would understand.
Using mm means most everyone (who knows metric) understands that in much more practical terms. A quarter of a tenth of thiiis much is a pretty damn tight fit.
Bold of you to assume that anywhere close to everyone who understands metric would know that 0.25 is a quarter of something.
Bold of you to assume that the country that still uses the Imperial system is the one that better understands fractions.
I didn’t say that imperial countries understand them better.
Micrometers is actually so common that it has a colloquial non-SI name of “micron”
According to wiki:
The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of biological cells and bacteria,[1] and for grading wool by the diameter of the fibres.[3] The width of a single human hair ranges from approximately 20 to 200 μm.
This
because it rhymes.
With?
The State of Indiana tried to define it to 1 digit by law.
https://en.wikipedia.org/wiki/Indiana_pi_bill?wprov=sfla1
Thankfully, the bill was never passed.
Ya know, this thread has inspired me. I’m a sound engineer, and find myself yelling “check one two three four” in the michrophone to test it all the time. I’m gonna start reciting the digits of Pi instead, and then as I learn them, I’ll progressively advance how many numbers of Pi that I use in my everyday job :D
I work at a library, though. I should probably just go with poetry or Douglas Adams or something, but this makes me sound much more impressive
You are already reciting some of the digits of pi. Just not the first ones.
Or some Douglas Adams poetry: Vogon poetry.
Oh freddled gruntbuggly,
Thy micturations are to me
As plurdled gabbleblotchits on a lurgid bee.
Answering my own question: I work in web development and my usual value for pi is the standard JavaScript Math.PI. JavaScript uses 64-bit floats, which are accurate to about 15 decimal places. But that’s how many digits the computer uses. For practical math, I don’t think I’ve ever needed more than 2 digits of accuracy in an equation involving pi.
Software Engineering. 16 sigfigs across 64 bits
Software Engineering too, I just use
std::numbers::pi. Don’t know how many digits it is offhand.I use M_PI and generally don’t care unless the device acts funny.
TIL a 64-bit float is accurate to 16 sigfigs.
Edit: actually, out of curiosity I decided to try and calculate it. I’ve very possibly done the wrong calculation, but what I did was log2(10x)=64, which works out to x≈19. Which isn’t 16, but is very close, and when you consider the way the float actually works it wouldn’t be too surprising that it was lose some information (the sign bit, for example, is immediately completely lost in this context).
A 64 bit IEEE float has 53 significant bits (the “mantissa” or “significand”), and log10(253) is 15.9546.
Yeah I wasn’t sure if it would be correct to throw out the exponent entirely or if it might end up contributing some amount to the final accuracy of the number. I hadn’t spent a lot of time thinking about the problem.
Yeah the exponent just allows you to represent lots of magnitudes, but it wouldn’t contribute to the accuracy because you basically have 1.xyz * 2exponent. So the xyz significand is the only part that counts for significant digits. Although I guess in some sense you are partially right, because the exponent exists it is assumed that the first bit is always one, since otherwise you would just adjust the exponent to the first one, so only 52 bits have to be stored.
Isn’t it just 15 significant figures then?
I would round up to 16.
Chip R&D. We only use 1’s, 0’s if management is feeling generous. There are no circles, no need for pi.
I work in healthcare and I’ve yet to use even a single digit of pi
What are you talking about? I constantly explain the calculus of the flow rate in the push IV drug I’m giving by going through the (pi)r^2 * h of the syringe, with emphasis on the dh/dy. All my patients love hearing it. They constantly thank me as I finish giving them the dilaudid.
I’m Australian. I normally manage a pie with 5 digits, unless it’s particularly crumbly or runny, in which case I will sometimes use 10!
I bet all the Americans reading this are now imagining you eating some gooey dessert like key lime pie or pumpkin pie with your hands.
If it’s anything like the little island off it’s east coast it will be steak and black pepper of a chicken korma pie
Steak and black pepper pie, now that’s what I’m talking about!
Peppersteak and Tomato ftw.
Chilli beef and cheese from a servo or gtfo.
I often find chilli beef on the dry side, I guess that it would mean that that pie may need only 5 digits and not the full 10 of a juicy steak pie
Fraser Island? Or Tasmania?
The ones slightly larger that tasmania…
Sacrilege!
Firstly 1, 500 km away is not coastal (if it was then the UK is an island off the coast of Iceland).
Secondly if anyone is off anyone else’s coast it’s the west island which is off our coast, not the other way round.
true enough
3628800?? thats a lot!
I find this comment absolutely hilarious.
I recognize your profile pic from a comment months back that was also a short, deadpan reinterpretation of the question that I found hilarious. I can’t for the life of me remember what it was of course.
Thanks for making me laugh!
I’ll be here all year :P
