Fox's Mercantile wrote:
___________________________


All units are inherently arbitrary.
The variable nature of them is only in the matter with which
they have been redefined for greater accuracy and repeatably.

It's not like a meter has suddenly changed from 39.370079" to
40". Or has varied from 30" to 40" over the years.


** Long time ago, it was decided to *define* the inch in tern of the cm.

1 inch = 2.54cm *exactly*.

so 1 foot = 30.48cm *exactly".

but 1 litre = 61 cu. inches is approximate, cos it goes the other way.




...... Phil