Let Moodle write the calculation formulas for you!  Bring your syllabus and come walk through the setup of the gradebook for your class.  Learn how to setup a gradebook with weighted categories, extra credit assignments, or to setup a category to drop to 2 lowest grades.  Other advanced features include import of grades from a spreadsheet (e.g. collected from graders), displaying grades as letters even if they are entered as numbers, and the student-centered grade reports (handy to use during meetings with individual students).