4 ms·

Slightly off topic, but my favorite units for c are feet per nanosecond. In those units c = 1 (plus or minus a couple of percent).

18nleung 9y ago
That's really interesting - only about 2% off. Conversion Here: https://www.wolframalpha.com/input/?i=speed+of+light+in+feet+per+nanosecond https://www.wolframalpha.com/input/?i=speed+of+light+in+feet...
contravariant 9y ago
It's even closer if you use a 'metric foot' of exactly 30 cm. Then you're only off by 0.1%.
- monochromatic 9y ago
  > metric foot Why is that a thing?
  - sixothree 9y ago
    Maybe because 30cm is very close to 12 inches.
  - contravariant 9y ago
    Not sure, but most of those 'metricised' units are leftovers from Napoleon's push to make everything metric.
letlambda 9y ago
Which leads to my favorite way to think about it. One foot per clock tick of a 1Ghz processor.
- stephengillie 9y ago
  Does this mean circuits in a 1 GHz processor can't be longer than 12 inches?
  - todd8 9y ago
    No information can travel more than a foot (11.8 inches) in a nanosecond. Grace Hopper used to give a talk where she held up a piece of wire that was that long to illustrate this limitation. [1] The first Cray computers were designed in a cylindrical shape to keep the signal wires short. [2] [1] https://www.youtube.com/watch?v=JEpsKnWZrJ8 https://www.youtube.com/watch?v=JEpsKnWZrJ8 [2] https://en.wikipedia.org/wiki/Cray-1 https://en.wikipedia.org/wiki/Cray-1
    - linker3000 9y ago
      'twas an annular shape! Ok..the backplane was annular
jeffwass 9y ago
I always like the fact that there are π seconds in a nanocentury (within half a percent)
bouvin 9y ago
No mention of the foot per nanosecond is complete without this seminal scene between the great, late Grace Hopper and David Letterman: https://youtu.be/1-vcErOPofQ?t=4m43s https://youtu.be/1-vcErOPofQ?t=4m43s
Cerium 9y ago
Mine are gigahertz * inches. 11.8ghz * in is the speed of light. Gives you a feel for it and is practical. Want to find an antenna length? Ghz*inches are your friend.
- boyce 9y ago
  That is great, never heard that one. Thanks

18nleung 9y ago

That's really interesting - only about 2% off. Conversion Here: https://www.wolframalpha.com/input/?i=speed+of+light+in+feet+per+nanosecond https://www.wolframalpha.com/input/?i=speed+of+light+in+feet...

contravariant 9y ago

It's even closer if you use a 'metric foot' of exactly 30 cm. Then you're only off by 0.1%.

monochromatic 9y ago
> metric foot Why is that a thing?
- sixothree 9y ago
  Maybe because 30cm is very close to 12 inches.
- contravariant 9y ago
  Not sure, but most of those 'metricised' units are leftovers from Napoleon's push to make everything metric.

letlambda 9y ago

Which leads to my favorite way to think about it. One foot per clock tick of a 1Ghz processor.

stephengillie 9y ago
Does this mean circuits in a 1 GHz processor can't be longer than 12 inches?
- todd8 9y ago
  No information can travel more than a foot (11.8 inches) in a nanosecond. Grace Hopper used to give a talk where she held up a piece of wire that was that long to illustrate this limitation. [1] The first Cray computers were designed in a cylindrical shape to keep the signal wires short. [2] [1] https://www.youtube.com/watch?v=JEpsKnWZrJ8 https://www.youtube.com/watch?v=JEpsKnWZrJ8 [2] https://en.wikipedia.org/wiki/Cray-1 https://en.wikipedia.org/wiki/Cray-1
  - linker3000 9y ago
    'twas an annular shape! Ok..the backplane was annular

jeffwass 9y ago

I always like the fact that there are π seconds in a nanocentury (within half a percent)

bouvin 9y ago

No mention of the foot per nanosecond is complete without this seminal scene between the great, late Grace Hopper and David Letterman: https://youtu.be/1-vcErOPofQ?t=4m43s https://youtu.be/1-vcErOPofQ?t=4m43s

Cerium 9y ago

Mine are gigahertz * inches. 11.8ghz * in is the speed of light. Gives you a feel for it and is practical. Want to find an antenna length? Ghz*inches are your friend.

boyce 9y ago
That is great, never heard that one. Thanks