As mentioned in the syllabus, the overall course grade for 18.06
is based on scores in the 3 areas of problem sets (24%), 3 hourly 
exams (42%) and the Final exam (34%).
The assignment of grades is a subjective process and the grade 
distribution varies from one semester to the next.
Typically, the average score in the 3 areas is used to identify
adequate, good, exceptionally good, and minimally acceptable
performance.
A concise description of these performance levels is given below.

A 
Exceptionally good performance, demonstrating a superior understanding 
of the subject matter, a foundation of extensive knowledge, and a 
skillful use of concepts and/or materials.

B 
Good performance, demonstrating capacity to use the appropriate concepts, 
a good understanding of the subject matter, and an ability to handle the 
problems and materials encountered in the subject.

C 
Adequate performance, demonstrating an adequate understanding of the
subject matter, an ability to handle relatively simple problems, and
adequate preparation for moving on to more advanced work in the field.

D 
Minimally acceptable performance, demonstrating at least partial
familiarity with the subject matter and some capacity to deal with
relatively simple problems, but also demonstrating deficiencies
serious enough to make it inadvisable to proceed further in the field
without additional work.