'This instrument simulates a Geiger Counter but without using actual radioactive sources. It is therefore completely safe. Powered by 240/12V.AC. Plug Pak - this microprocessor based instrument can display the counts of particles leaving an imaginary r/a ''source'' and also can display the number of r/a particles remaining inside the ''source''. The concept of half-life is easily demonstrated and the random nature of the particle counts can be shown. The unit is used also in Maths in the study of ''random numbers'' and statistics. '