The error Tuesday was classified a B, the third B-grade mistake since Oct. 1 at the Chicago Center, one of about 20 regional traffic control centers around the country.
According to research at Johns Hopkins, staging and grading mistakes occur in about 20 percent of specimens.
By comparison, the center was responsible for only one grade-B mistake in all of the previous 12 months.
One case was included in the study with a baseline level of CPK grade 2 by mistake and the patient was withdrawn from the study.
Obviously there is a positive correlation between the two but you should never mistake grades as a perfect representation of intelligence.
This somewhat unconventional exercise produces wrinkled brows and guarantees errors in a student at the end of ninth grade, but the mistakes don't matter.
When I was in 7th grade, I made the mistake of watching the horror film, "The Ring".
Prof Dylan William of University of London's Institute of Education said reducing the number of grades would be a mistake.
"From my first appearance in the quarter," he wrote, "my French was no worse than that of a White Russian or a Czech, and I rose rapidly and successively through the grades of being mistaken for a Hungarian, German Swiss, Alsatian and Belgian from the Flemish-speaking provinces".
He knows, from working in his own stores, how eager men are to try, yet how afraid they are of making a mistake (see sixth grade, above).
Grade added that the biggest mistake of his career was turning down The X Files when he was chief executive of Channel 4. "We said, 'This will never run - it's complete garbage,' which shows you how wrong you can be.
