Forgive me if this is common knowledge, but I have just discovered the Supermemo concept and would like to use it more.  I have started a course (without paying yet) and the course is not allowing me to progress further.  I have completed about 50 "questions".  Do I need to pay to gain access to the rest of the course or does the supermemo program only allow me to learn a certain amount per day? Does paying release more features like editing?  Thanks for any responses!