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.