The 90-80-70-60 scale... what gives?

In the US of A, it is well known that, on most tests, if one scores between an 80 and 90 percent, one earns a letter grade of a B. Ummm... okay. Why? Why not 60 to 80%? Why not some other arbitrary range?

Here is more of the "standard" scale:

• 100-90% = A - which typically means "excellent"

• 90-80% = B - which typically means "good"

• 80-70% = C - which typically means "satisfactory"

• 70-60% = D - which typically means "poor"

The last of these letters is F which typically means "Fail". Of course, that means that the F scale goes from 0% to 60%. So, you're trying to tell me that the F range is 6 times larger than each of the other ranges? Why is that?

This also means that the range for "excellent" is the same size as the range for "good". Does that make sense?

My point? These ranges seem totally arbitrary and I can see no benefit to the student or to my teaching in having to use such ranges.

This grading scale also begs the question: Percent of what? Now, in math classes, it usually means the percent of points a student has earned against the possible number of points. So, if a test is worth 40 points and I get 30 of those points, then I get a 75% and thus a C. So you're telling me that I understand 75% of what I was tested on and this is satisfactory? What if I that 75% represents the top score on the test? Then what does that mean about my "satisfactory" grade?

Even weirder is that this scale gets used in other disciplines. I write an essay in English. My essay is "good", but not "excellent", so I should get a B, I guess. But, how in the world could one possible assign a number to my essay.

Anyway, I give this post a 77%.