By the definition of using light you can quanify a foot or yard by a
division of that length. In a way the scientific advances that allowed
the modern definition of the metre also made the most accurate yard length
ever, thanks to the very concept of the metre.
Accurate in relation to what?
But what I am trying to say that at some point the yard was compared to
the metre to set-up a conversion factor.
It would be interesting to know how they actually went about doing this.
Did they physically take a metre stick to the official yard at Trafalgar
square?
I doubt it.
A prototype kept out in the open exposed to the elements is hardly sensible
for the purposes of modern metrology.
With all due respect you haven't grasped the key point here. The statement
"1 yd = 0.9144 m" is not just a conversion factor.
It is a *definition* of the term "yard".
The yard has no other form of existence in the modern world, it is numerical
only.
Phil Hall
