I am new to the forum. Just purchased a GQ GCM-300 and live near the beach...planned to go down and do some testing. However, with such a spike today, (350-400) this means I should probably stay inside? What does this really mean? (my only notion is that >100 CPM sustained is 'bad')

Anyone can explain all this, would appreciate it (especially difference in risk between actual beach/coastline edge vs. just at my home where the CPM seems to average for three days only 16-20 CPM) ... although on this cheap counter.

Last question, station 354, if that's EPA station, if they are reading these levels w/ more sophisticated tools, isn't that cause for concern?

A real quick answer. EPA has different equipment and is using Gamma range #5, total different than the GMC-300.
Most of your questions are already answer in Letters to Netc on the Netc.com Forum.
Harlan

You would be surprised to see how well this "cheap counter" can really detect the radiation when used outside on an air purifier. Below see my outside purifier radiation stations graph compared to an EPA site.

The problem is too few people care enough or understand the big difference it makes outside on an air purifier, so they leave it inside and only see the large gamma only spikes and falsely believe their inside unit is giving them an accurate measurement of the outside radiation.

Guys, thanks both of you for your posts... I will dig in and read up on the site...

I just left the beach in San Francisco within site of the GG Bridge. For what it's worth, over an hour walking here and there, setting the GMC-300E on the rocks, on gravel near water, above the sand... Average over the hour is 18 CPM with highest spot reading 25 CPM. That's in line with what I'm getting for background at my home in SF. That seems like a good thing, but doesn't seem to jive w the warning on the map and the very high EPA monitor... I guess I have a lot to learn, but that was encouraging to me.

Will read your posts when I get home. Btw, what do you mean by 'on an air purifier'?

Thanks