When learning, teaching oneself, or training a class in Morse Code sending using a hand key, how can acceptable quality be scored (other than the letters being correct terms of dot-dash sequence)? There a big difference between the dots being a bit shorter than the dahs at widely varying WPM between characters and words, and nice perfect 3:1 timing at an exact 13 WPM, etc. What objective metric should be used to determine a "passing score"?
(Objective metric requested because many humans are too good at "hearing" the expected message even if there were errors or near errors in the coding. And it's not hard to measure key open/closure timings to millisecond precision for use in any objective scoring algorithm.)
Was there a metric used for acceptability quality in any country back when Morse Code sending was tested as required part of a license exam?