I believe that Peter Charlie's device was measuring in microsieverts (µSv/h) . . .

Here is some information, from where I found the chart -- http://www.gavinshoebridge.com/news/basic-guide-to-radiation-levels-in-%C2%B5svh-and-msvh/

Radiation levels can be a very complicated thing to figure out, with alpha, beta, and gamma rays to understand. I won’t go into details, or you’ll have 10 pages of reading to do, so I’ll just post a chart of what levels of radiation are safe to live in - and when it’s time to start running!

So, here’s a simple, plain-English chart of radiation doses in millisieverts (mSv/h) and microsieverts (µSv/h) per hour. Most dosimeters (the handheld Geiger counters that measure your body’s “Dose”) operate in these units.

It’s quite a simplified chart, and it helps to know that radiation gets more dangerous, the more your body gets. If you get a big amount of radiation in an hour, it’s more hazardous than getting the same amount over an entire year. This chart is measured in an hourly dose, just like what your meter will probably show on the screen.

More to follow on this subject.

Jeff