Available Memory and freeMemory on Help & About page

A quick and possibly dumb question! If I go to the Help & About page it gives me an indicator of the memory used:

So that says I’ve used 46 MB out of 328 MB available, right? I assume that 328 MB is the committed heap, but I’m not sure. Anyway, if I click on view details, I see these same figures:

Except here it seems to be saying that the 46 MB (48343192 bytes) is free memory. But this is the same number being reported as used above? Am I all turned around or is there a typo here?