Class Enrollment vs. Enrollment Count

Under "Enrollment Measures," what is the difference in Class Enrollment and Enrollment Count?

On a positive note, I was able to create an enrollment census view today where the results from SAH fall within a comfortable margin of error when compared to Blink queries for all of the years from 2007 through FA18 (yay!).  Years prior to 2007 seem low (increasingly low with each year).