Hi Tamara.
When using scales for grading, it is important to realize how mapping from a scale item to a grade works (generally in Moodle, not just Workshop).
Your scale defines five items. It is assumed that the lowest (first) scale item maps to the worst possible performance and it maps to grade 0. The highest (fifth) item represents the best performance which maps to grade 100%. In other words, your scale is transferred to a grade like this:
- Nothing selected - No grade
- Item 1 selected -> 0%
- Item 2 selected -> 25%
- Item 3 selected -> 50%
- Item 4 selected -> 75%
- Item 5 selected -> 100%
Whereas you seem to have assumed that Nothing selected maps to 0% and the lowest scale item gives 20% grade etc.
This is important to keep in mind when designing scales and rubrics where similar logic is implemented.
So in your case, only the first aspect is considered (other two having the zero weight do not affect the grade) and the first one "Item 4" is mapped to 75% of the max grade 5 which gives 3.75. Formally:
(4 - 1) / (5 - 1) * 1 + (5 - 1) / (5 - 1) * 0 + (5 - 1) / (5 - 1) * 0
--------------------------------------------------------------------- = 3 / 4 = 75 %
1 + 0 + 0
The "Calculated grade for assessment" is another (big) topic. It is the Workshop's estimate on how well this particular peer-assessment lines up with all other assessments of the same submission. It is not always accurate (especially with low number of reviewers per submission) and teachers are encouraged to interpret it accordingly.
More details can be found on https://docs.moodle.org/en/Workshop_grading_strategies and https://docs.moodle.org/en/Using_Workshop#Grade_for_assessment