Professor Alois Brandl (1855 - 1940), founder of the German Shakespeare Society and chief Professor of English at the University of Berlin stated
"that the English of Americans was not only improving, but was already as good as that of our English cousins."
Anglo-Saxon scholar Professor W.W. Skeat (1835 - 1912) of Cambridge University, agreed with the German savant and went on in greater detail.
No mention whatever was made of the precise unit of measure needed to reach such conclusions.
Read about the Canadian Preferences in English...