I wish this chart did a little more to explain the meaning of the units. A big red dot corresponding to 559 nano-greys / hour (the highest reading when I viewed the chart) probably doesn't mean anything to most people.

That rate is about 2.33 x the world average background radiation level (ignoring quality factors and assuming 1 GY = 1 SV) and listing that alongside the raw units would be helpful.

- http://en.wikipedia.org/wiki/Background_radiation