The numbers below are minimal thresholds to achieve a letter grade, hence in the 1000pt scale, you need an 800 to get a B-. 799.999 does not reach this threshold and consequently is a C+.
100 pts 1000 pts
A 93 A 930
A- 90 A- 900
B+ 87 B+ 870
B 83 B 830
B- 80 B- 800
C+ 77 C+ 770
C 73 C 730
C- 70 C- 700
D+ 67 D+ 670
D 63 D 630
D- 60 D- 600
F< 60 F< 600
I know grades can be disappointing. I wish I didn’t have to bother with them as I explain in a blog posting about The Travail of Grading.