Statistics about the past?

I am new to FreePBX. I installed FreePBX 12 and Asterisk 13.2 on a Centos 6.6 machine.
I mainly navigate the interface on a Firefox 36 browser.

I am rather perplexed by the statistics box on the System Status page.

I can only see statistics for the last minute or hour. If I select Day or Month the graph disappears.
There are no x axis spacers to show what the time scale is.
I cannot understand if the statistics are real time only (only available if the browser is kept open), or whether they should be saved somewhere, so the browser can retreive them in the future.

There is no warning or error on the graph to say it cannot access MySQL or whatever.
I read in another post that the statistics are kept in MySQL.

Is this an issue or the expected behaviour?
If I should be able to see data for the past, where do I start debugging this issue?

this post from the FreePBX news pages:

FreePBX’s new dashboard logs data even while you are away from your PBX so you
can pinpoint exactly when you are (or were) having problems as far back
as a month from now.

To me this sounds like these statistics are really FreePBX’s and not anywhere else in the system.
If this is true, it makes sense that you can only see data from the time you opened the interface.