I feel like I answer this question all the time
When I first developed the database, I didn't think forward and forgot to include "year" in the tank log. Now, it's too late, as every user would have to define the year for each of their tanks -- it's just impossible now. The graph just rolls over and averages in to past years, which will eventually give you an idea of what you're likely to reach in a given month, or what you ought to try to beat. If you beat your previous years' average, you'll raise your LMPG.