What exactly is "exact" (was Clean Singleton Docstrings)

[Rustom Mody]

On Tuesday, July 19, 2016 at 12:28:36 AM UTC+5:30, Marko Rauhamaa wrote:
> Ian Kelly :
> 
> > Okay, so how is that wavelength defined?
> >
> > If you needed to mark a meter stick, and all you had was the
> > definition of c and the second, how would you do it without measuring
> > anything?
> 
> I wouldn't be measuring a meter stick. To measure, say, the height of a
> desk, I would bring in some caesium and shine its radiation from the
> desk level down to the floor. By counting the ebbs and flows of the
> radiation as it leaves the nozzle and strikes the wooden floor I make
> the approximage height measurement.
> 
> However, I know *exactly* how long a meter is without making a
> measurement.

I recollect — school physics textbook so sorry no link —
that in the Newton gravitation law
f = -GMm/r²

there was a discussion about the exponent of r ie  2
And that to some 6 decimal places it had been verified that it was
actually 2.000002

I dont remember all the details
Just that something so obviously to a layman mathematic/analytic as 2
for a physicist may be something calling for experimental verification
ie synthetic/scienceic:
http://plato.stanford.edu/entries/analytic-synthetic/