DISCLAIMER: Please see the default guaranteed grading scale here. That is, you are guaranteed to get no less than the grades listed there for the corresponding earned percentages. Depending on the class performance, I reserve the right to modify this scale (in your favor) at the end of the quarter.

For example, if the quarter were over today, since the grades so far are lower than expected, I would probably modify the default grading scale in your favor as follows:

This would give approximately:
85%->3.5
80% ->3.1
72%->2.5
66%->2.0
53%->1.0
50%->0.7