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from the that's-the-combination-to-my-luggage! dept.
https://www.jpl.nasa.gov/edu/news/2016/3/16/how-many-decimals-of-pi-do-we-really-need/
Earlier this week, we received this question from a fan on Facebook who wondered how many decimals of the mathematical constant pi (π) NASA-JPL scientists and engineers use when making calculations:
Does JPL only use 3.14 for its pi calculations? Or do you use more decimals like say: 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588174881520920962829254091715364367892590360
We posed this question to the director and chief engineer for NASA's Dawn mission, Marc Rayman. Here's what he said:
(Score: 2) by Zinho on Thursday August 15 2019, @04:07PM
Unless you are using a decimal-marked inch scale (like the 1:10 side of an engineer's scale [wikipedia.org]) then you'll have a mismatch between the implied precision of the measurement you took and the exact decimal representation of that measurement.
When you're using your tape measure and read to the 7/32 mark, your measurement's precision is +/- 1/64. The decimal representation of 7/32 (0.21875) appears to have a precision of +/- 0.00005 inch; in reality it's more like +/- 0.01 inch or +/- 0.02 inch (truncating or rounding 0.015625). This is the exact problem we have with decimal-to-binary number conversion, and there's not a practical solution.
If you're keeping track of all 6 decimal places worth of those 1/64 inch measurements to avoid losing accuracy due to rounding after number conversion, feel free. Especially if you're getting high-quality results, don't think I'm trying to stop you. If, at the end of your calculations, you're shifting the result into a CNC machine for the final cut it's important for your mental health to realize that truncating or rounding at the 1/1000 inch place is all the precision you've gained for your effort, and the machine won't benefit from any extra digits.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin