they switched the panel interface about a month ago, and it's TERRIBLE!
they bill your usage for the combined total of "actual" ram usage and "cached" ram usage, however the new graphs only show ACTUAL usage, so you have no idea what you are really using. they also took away the ability to see more than a weeks worth of history, which is equally as frustrating!
what you are seeing is the actual usage for about the last 24 hours from what I can determine and the daily "average" for the last 6 days before that. not particularly helpful.
bug chat support, they can pull up some of your actual number totals.
maybe if enough of us bug them enough to be a pain they'll fix it?!
I've been bugging support regularly, and all I get is "they are working on updating the the panel again"...so they know it sux, they're just not helpful about it!