Grades will most likely (but not always) be computed on the following scale:
How to use the WEIGHTED GRADE column: This column can tell you the maximum possible score that you can still get in the course. If the total % currently in is, say, 30%, and your weighted grade is 18%, then that means you are 12% (30-18) short of the maximum. So your maximum possible score for the entire course is 100-12 = 88% = B+. This assumes you don't lose any more points for the rest of the term (which is unrealistic for any human). So just treat it as a way to figure out what is still mathematically possible.