The files with suffix "dist" are distributions for points for individual items -- for example total.dist contains the distribution of total points so far (and midterm.dist and final.dist will contain distributions for the midterm and final exams).
The file total.dist contains the distribution of total points.
The course grade is determined by total points according to the table:
90% of possible points guarantees an A-
80% of possible points guarantees a B-
70% of possible points guarantees a C-
60% of possible points guarantees a D
These cutoffs may be lowered slightly, but they will never be raised.