On Wednesday, 20 March 2019 17:18:23 UTC, wrote:
On Wednesday, 20 March 2019 11:43:48 UTC, whisky-dave wrote:

I like the speed of light as measured to be *about* 1 foot per nanosecond .
- in fact, it is 0.9835710564304 ft/ns.

Yeah like I said .


It has not been possible to measure the speed of light since 1986 or earlier;

yes it has , it;s been in physics books long before then.

by/in 1986 it was defined in SI as 299 792 458 m/s precisely. The experiment can still be done, but, given that the second is well-defined and accurately-disseminated, the result is a calibration of whatever length standard was used in the work.

Yes so, but for most it was accurate enough even in the 18th century.



Be warned that from May 20th 2019, the definition of the kilogram will no longer be that it is the mass of a Pt-Ir cylinder cherished in Outer Paris. See in https://en.wikipedia.org/wiki/Kilogram !

Yes I know I heard all about it.
But it's not going to make much differnce to the majority of us is it.
I also know the freezing point of water isn't 0C it's 0.01C IIRC.

But you can have stationary/ none moving water that is -4C