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What field do you work in, and how many digits of pi do you use? (lemmy.world)

submitted 7 months ago by [email protected] to c/[email protected]

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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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[–] HobbitFoot 9 points 7 months ago* (last edited 7 months ago) (1 children)

Structural engineer, and it depends. If I am doing structural or quantity calculations, I can get away with 3.14 (3 digits).

If I'm dealing with survey coordinates defined by horizontal curves, I'll have to use at least 10 digits.

[–] [email protected] 5 points 7 months ago (2 children)

So do I have this right - if you think about the building being structurally sound you can get away with more error than if checking whether you're accidentaly on the neighbour's plot of land?

[–] [email protected] 11 points 7 months ago

Not a civil engineer, but an engineer here, if you're doing structural soundness, you usually apply a generous margin of error, so it doesn't have to be that tight, you're building it 3 times as strong as needed anyway.

While if you're calculating where your plot is, you don't want to leave a few meters empty or go past a few meters "just to be sure".

[–] HobbitFoot 8 points 7 months ago

Yes.

There isn't that much benefit to knowing if something is 4.5672% overstressed compared to being 5% overstressed. There are also some cases where the method of calculating demand or capacity isn't that precise; the design code will show the simple equation but have a more complicated equation that better models what is happening in the commentary.

In contrast, some surveying is dealing in a state's coordinate plane. This can be very precise, with some measurements provided down to the 1/10000 of a foot to keep error down when they measure it in the field. In that case, you need to be more precise.