This link will take you to a document that discusses Knols. Knols are a unit of actual learning as demonstrated by mastery and are a replacement for seat time as the main unit of measurement of learning.
The Khan Academy Exercise and Assessment syste
The exercise and assessment system that is provided for free is one of the most complete and powerful exercise and assessment systems ever developed. And it is free. The system allows for the first time the actual measurement of learning as it is happening. This video provides more details of this incredible tool.