Checked with a different system. Windows 7 Ultimate 64, running the same version of FF and got the same result. IE on that system looks like yours. Looks to me like a bug in the FF browser or a bug in the site coding that the browser is ignoring or skipping or something. Oh well, hopefully you can figure it out. No worries, been like that a while, just occurred to me to say something today. lol
That is odd. Everything looks fine for me in Firefox 5.0.1 on Windows 7 Ultimate 64. I see the missing data point in your screenshot, but I have no idea what could be causing it.
You could try clearing out your Firefox cache. There's on off-chance you have an older version of Highcharts in your browser cache--and this bug has been fixed in the newest version. Here's the version we're currently using:
Weird. It was a cache issue, the version was 2.1.4, not 2.1.5. Funny that it would have been wrong on the other system, but whatever. After doing a hard refresh on that page it works fine now. Strange though.
I have a couple cases where one might want to graph their own fuel costs independently from the national average.
First, some of us run Biodiesel instead of petroleum based fuels. Our cost fluctuations are different from most gassers.
Second, some people make their own Biodiesel, and would probably end up tracking their costs differently. If they've gone through the work of assigning a $/gal figure to their homemade fuel I could see them wanting to see a graph of their costs.
Third, users who are optimizing for fuel cost may want to compare their own average against the national average.
However, independent of any particular use case, having generic support for graphing any metric you're already exposing in the mini-stats means that users will be able to create combinations of charts that we can't yet imagine. In my mind that alone is the biggest argument in support of implementing touvang's request.
All that said, you can consider this a vote for a feature I think would make fuelly even more awesome. I hope you can find room on the roadmap for it.