Basic documentation on Certainty-Based Marking (CBM) is at https://docs.moodle.org/27/en/Using_certainty-based_marking .
This plugin displays result reports (for teachers) that properly summarise student performance in quiz attempts that use CBM behaviour. Optionally, scores on individual questions can be displayed. Percentages can be calculated on the basis of either just those questions for which a student has entered a response, or the whole quiz. For example, 100% correct on half of the questions - those which the student has chosen to work on - can be shown as 100% rather than 50% correct. This is appropriate when a student uses the quiz for self-testing, choosing just questions relevant to current learning or self-assessment needs.
The plugin was developed alongside improvements in CBM behaviour that are included in core code in Moodle 2.6+. Version 1.2 can be used with Moodle 2.3-2.6. Version 2.7.02 is required for Moodle 2.7 onwards (at least to Moodle 3.0). It really should be in core Moodle.
This plugin doesn't affect feedback of information to students. CBM feedback in student Reviews was introduced in core Moodle 2.6, though this is much improved by installing patches (including for earlier versions 1.9+) available at http://TMedwin.net/cbm .
If you want Moodle Grades to correspond to CB Accuracy (0-100%) for comparison with conventional accuracy rather than to the total of CBM marks (see https://docs.moodle.org/30/en/Using_certainty-based_marking ) then use the code modifications and plugin available at http://TMedwin.net/cbm . Otherwise Moodle Grades range up to 300% based simply on the total CBM marks and have a non-linear relation to conventional accuracy, .
Please report any issues to me: Tony Gardner-Medwin (firstname.lastname@example.org)