This article is from the RSC/UKSC Cricket FAQ, by Ganesh with numerous contributions by others.
John Hall:
You're assuming it's decided by some objective method,
rather than some cricket journalist or statistician
simply going by their own fallible opinion of speed.
Bowler W____ (classified as fast medium)
bowls faster than Bowler G_____(classified as fast)!
How can one only be a fast medium yet the other a fast bowler?
See John's explaination above.
 
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