I just ordered the 500+ because I always wanted a gieger counter to add to my electronics tool box. The prices of these units puts them well in the consumer price range so now was a good time. I'd like to have a test source but honestly the price of tiny pieces of uranium ore is ridiculous. What are you guys and gals using? Also could someone recommend a reliable website for radioactive samples
Take a household item like garden fertilizer, or any other product with lots of Potassium in it. Read my "GeigerLog Potty Training ..." for details; downloadable from here: https://sourceforge.net/projects/geigerlog
And better than with any strange Uranium or else source, you know what you have and can do real physics experiments!