The Electronic Distance Meter uses electromagnetic waves to measure the distance. Originally these used radio waves for the measurements but later models all use laser / infrared light. The EDM originates from surveying but is now also used (in a small package) for home improvement. The optical EDM in surveying is used together with a thedolite and then becomes a tachymeter or total station. In home improvement it replaces the tape measure. Most EDM's in my collection are from Wild Heerbrugg.