Weight is only available with “Weighted mean of grades”. For the “Simple weighted mean of grades”, the weight is taken from the grade item’s maximum grade. A weight is used to give a grade item more or less importance in the computation of the category total or average, compared with the other items of the same category.

Extra credit replaces grade item weight if the aggregation method is “Mean of grades (with extra credits)”, “Sum of grades”, or “Simple weighted mean of grades”. The effect of extra credit is different in each case, hence some confusion:

- Mean of grades (with extra credits): A value of 0 does nothing. Any other value is used to multiply the grade and add it to the total after the computation of the mean. This grade is not used in the computation of the mean, however, only added afterwards. Additionally, this cannot bring the category total over its maximum grade unless grades over 100% are enabled by the site administrator (since 1.9.5). This grade item is not counted either in the denominator used to compute the category mean.

- Sum of grades: Extra credit is a checkbox, not a number. Normally, with Sum of Grades, the category’s maximum grade is the sum of the maximum grades of all its grade items. If one of them is set as “Extra Credit”, however, its maximum grade is not added to the category’s maximum grade, but its grades will be. This way it is possible to achieve maximum grade (or grades over maximum if enabled by the site administrator) in the category without getting the maximum grade in all the grade items.

- Simple weighted mean of grades: Extra credit is a checkbox, not a number. The “Extra Credit” grades are counted in the numerator used to compute the category mean, but not the denominator. See here for more information.