Reconnaissance meters IM-4175 for radiation. Radioactivity meters / Geiger counter IM4175 Royal Netherlands Army from the 60s/70s Capacity: 0 - 500 Rad/h, 0 - 50 Rad/h, 0 - 5 Rad/h, 500 x 10 CPS (for external probe), 50 x 10 CPS (for external probe). 3 different scales. Weight 2 kg, dimension: +/-20 x 18 x 14 cm Operates on 2 batteries of 1.5 volts. Complete and working. We cannot perceive radioactivity with our senses, it is odourless, colourless, tasteless, invisible and we cannot feel it. With certain equipment one can measure the effects of ionising radiation on atoms and molecules. The most famous device is the Geiger counter. This device bears the name of one of its inventors: the German professor Hans Geiger developed the first Geiger counter in 1928 together with his colleague Walther Müller. You sometimes speak of the Geiger-Müller counter.