This easy-to-use combination instrument makes professional measuring techniques available for home use. The only instrument in this price range to detect both mains current (50 Hz) and the frequency of overhead railway power lines (particularly important environmentally), which can often be detected several kilometres away from railway lines. The natural harmonics of mains current, e.g. from transformer stations, are also accurately detected. Another unique feature is the high resolution, which allows meaningful comparisons with the strict environmental limits.Equipped with a professional filter to distinguish between railway and mains current and harmonics between 2 kHz and 100 kHz (energy-saving lamps, switching power supplies, etc.) which experts consider to be particularly important in terms of their biological effects.