Another great story of the Metric vs. Imperial translation problem, this one
many years old.  If you have ever had any serious involvement with
telescopes used for astronomy, you have encountered the little eyepieces
that usually come with less expensive imported scopes.  They have a diameter
of .965 inches, a bastard size in any measurement system.  Why?  Simple
answer.  In the late 1940's as Japan was rebuilding their optics industry
they wanted to make telescopes to sell in the US.  At that time most amateur
astronomers in the US used eyepieces that were 1 inch in diameter so that
was the standard adopted by the Japanese optics industry.  Standards were
published and production was well on the way before it was noticed that
someone had used 24.5 instead of 25.4 as the conversion factor.  But a lot
of product was already in the pipeline and so to this day the cheaper scopes
from the Far East will likely have an eyepiece that is .965 in diameter.