This evaluation type can be used to provide automatic negative feedback on the student’s answer. It can therefore only be used in negative feedback rules. This feedback type is particularly good at pointing out minor mistakes in the student’s answer, see the examples.

The Definition field should have an expression that the student’s answer should be compared with. Generally, this is the solution.

The field Precision can be used to indicate a minimum percentage (between 0 and 100) of similarity between the Definition field and the student’s answer at which the feedback kicks in. The higher the percentage, the fewer mistakes a student can make for the feedback to kick in. The default Precision is 0. There is no clear guideline on what the Precision should be for the expression in your Definition field. This is a matter of testing out different values until the feedback rule responds appropriately. If the student’s answer is exactly the same as the expression in the Definition field, this feedback rule will not kick in.

Examples:

**How it works**

The system makes two trees: one for the feedback rule Definition and one for the student’s answer. These trees contain all operations and atoms that the system finds in the answers. These trees are then compared, and if the similarity is higher than the Precision, then the feedback rule will go off. We will not go into detail on how the trees are compared exactly.

Example: