What is Mastery In Reviewing? The books and videos all describe it as,

Looking at jhana and its factors in retrospective knowledge

What does this mean exactly? Is it going over the events that happened during the jhana?  there anything specific you suppose to do?
I think you go over the meditation, what you did, how, compare with other meditation sessions to find out how to easily get jhana. 

I did this and this and I got that result and the other time I did that and that and got another result. 

So in time you get better at recognizing the factors and how to get in jhana.