4 ms·

Interesting other take I've seen: The continued fraction of Pi is [3; 7, 15, 1, 292, ...] The 292 is a pretty big number, so at that point the fractional appro

Interesting other take I've seen: The continued fraction of Pi is [3; 7, 15, 1, 292, ...] The 292 is a pretty big number, so at that point the fractional approximation is very good. 355/113 is good enough for anything you're doing on planet earth.

lisper 6y ago
Just for the record, 355/113 = 3.14159292... and pi = 3.14159265...
deleted 6y ago
[deleted]
hanoz 6y ago
> 355/113 Just memorize those six digits to get you four digits beyond the three that everybody knows.
- fsckboy 6y ago
  i just memorized it as / 1 1 3 3 5 5 / where you start with the denominator and circle back.
  - cgriswald 6y ago
    So you've got to remember three digits, the fact they are doubled, the place to start, and the place circle back (or deduce any of those). Or you can remember 1592 as the year Trinity College in Dublin was founded. You didn't know that? You probably won't forget now.
    - function_seven 6y ago
      Ha. I don't think I'll remember '1592' directly. Easier to remember the offset of '+100' and combine it with my existing knowledge of who sailed the ocean blue.
  - AnimalMuppet 6y ago
    Think of it the way we wrote division in grade school, like: ___ 113|355
- hnracer 6y ago
  Memorize six digits to get seven back?
- mdiesel 6y ago
  I've got Pi memorised more precisely than 355/113 as well for no good reason, and for engineering applications it doesn't serve any purpose. But the fraction is weirdly close and that's interesting for other (more academic) reasons, such as explaining why plotting primes in polar coordinates looks like a pattern: https://www.youtube.com/watch?v=EK32jo7i5LQ https://www.youtube.com/watch?v=EK32jo7i5LQ
dublin 6y ago
3.1415927, which I memorized in 10th grade (just a hair more accurate than 335/113) has always been more than adequate for every engineering task I've ever had to engage in - including those in the aerospace industry (both rockets and planes/jet engines), and the oilfield industry (all kinds of stuff, including precision sensors).
Retric 6y ago
Some people do work at vastly higher levels of precision. The electron g factor has been experimentally deterred as -2.00231930436256 +/- 0.00000000000035. NASA on the other hand uses corse corrections rather than trying to active insane precision with rockets. It’s simply more efficient.
- guenthert 6y ago
  Also because the course cannot be exactly computed in advance. The environment in space, even far away from earth, isn't an ideal vacuum and particle density will depend on solar activity. Then there are effects which are (or until recently were) ill understood, like the pioneer and voyager anomalies. I suspect however, that the effect of not quite perfect burn schedule and burn intensity of the propellant has a much greater effect. And how well do we know the mass of e.g. Jupiter really? GIGO.
  - CydeWeys 6y ago
    > I suspect however, that the effect of not quite perfect burn schedule and burn intensity of the propellant has a much greater effect. This is the real answer right here. Rockets have all sorts of uncertainties in them. You have the measurement uncertainty in exact orientation and the measurement uncertainty in the acceleration and thus total thrust delivered, all on top of the physical uncertainty in exactly how powerfully your engine is going to burn, and for how long. Remember, there are physical valves that need to open and close to control propellant flow, and there are chaotic perturbations in the conditions inside the combustion chamber. You simply cannot remotely achieve a perfect delta-v in a perfectly specified direction; there are uncertainties on both.
- gnramires 6y ago
  You are right, one can imagine a chaotic system where any deviation from a path will be amplified and have significant costs in the future (i.e. space navigation in realistic gravitational fields), then extreme precision may make sense (where an error might be amplified millions of times further in the path).

lisper 6y ago

Just for the record, 355/113 = 3.14159292... and pi = 3.14159265...

deleted 6y ago

[deleted]

hanoz 6y ago

> 355/113 Just memorize those six digits to get you four digits beyond the three that everybody knows.

fsckboy 6y ago
i just memorized it as / 1 1 3 3 5 5 / where you start with the denominator and circle back.
- cgriswald 6y ago
  So you've got to remember three digits, the fact they are doubled, the place to start, and the place circle back (or deduce any of those). Or you can remember 1592 as the year Trinity College in Dublin was founded. You didn't know that? You probably won't forget now.
  - function_seven 6y ago
    Ha. I don't think I'll remember '1592' directly. Easier to remember the offset of '+100' and combine it with my existing knowledge of who sailed the ocean blue.
- AnimalMuppet 6y ago
  Think of it the way we wrote division in grade school, like: ___ 113|355
hnracer 6y ago
Memorize six digits to get seven back?
mdiesel 6y ago
I've got Pi memorised more precisely than 355/113 as well for no good reason, and for engineering applications it doesn't serve any purpose. But the fraction is weirdly close and that's interesting for other (more academic) reasons, such as explaining why plotting primes in polar coordinates looks like a pattern: https://www.youtube.com/watch?v=EK32jo7i5LQ https://www.youtube.com/watch?v=EK32jo7i5LQ

dublin 6y ago

3.1415927, which I memorized in 10th grade (just a hair more accurate than 335/113) has always been more than adequate for every engineering task I've ever had to engage in - including those in the aerospace industry (both rockets and planes/jet engines), and the oilfield industry (all kinds of stuff, including precision sensors).

Retric 6y ago

Some people do work at vastly higher levels of precision. The electron g factor has been experimentally deterred as -2.00231930436256 +/- 0.00000000000035. NASA on the other hand uses corse corrections rather than trying to active insane precision with rockets. It’s simply more efficient.

guenthert 6y ago
Also because the course cannot be exactly computed in advance. The environment in space, even far away from earth, isn't an ideal vacuum and particle density will depend on solar activity. Then there are effects which are (or until recently were) ill understood, like the pioneer and voyager anomalies. I suspect however, that the effect of not quite perfect burn schedule and burn intensity of the propellant has a much greater effect. And how well do we know the mass of e.g. Jupiter really? GIGO.
- CydeWeys 6y ago
  > I suspect however, that the effect of not quite perfect burn schedule and burn intensity of the propellant has a much greater effect. This is the real answer right here. Rockets have all sorts of uncertainties in them. You have the measurement uncertainty in exact orientation and the measurement uncertainty in the acceleration and thus total thrust delivered, all on top of the physical uncertainty in exactly how powerfully your engine is going to burn, and for how long. Remember, there are physical valves that need to open and close to control propellant flow, and there are chaotic perturbations in the conditions inside the combustion chamber. You simply cannot remotely achieve a perfect delta-v in a perfectly specified direction; there are uncertainties on both.
gnramires 6y ago
You are right, one can imagine a chaotic system where any deviation from a path will be amplified and have significant costs in the future (i.e. space navigation in realistic gravitational fields), then extreme precision may make sense (where an error might be amplified millions of times further in the path).