This is the most popularized method. You must get some percentage of the points possible for an A, some lesser for a B, and so on. In fact, for reasons I discuss in my test page , that is not at all true. This is how most graduate courses, and many small undergraduate classes, are graded. There is no consensus about what grades mean.
Some professors hand out As like candy, while others are proud of their misanthropy.
If you asked a professor what a grade means, he may or may not be able to give an intelligible response. The defenders of the status quo usually rationalize that over many courses, students tend to get the GPAs that reflect their performance. So you one should not put all that weight in a single grade. Thoughts A grade is only a measure. If an education is what you wanted, and what you got, then you have succeeded in your effort.