The tachymeter can be used to measure both angles as well as horizontal and vertical distances. Depending on whether it is an optical or electronic tachymeter a special staff or prism is required. The optical type uses an elaborate system to convert the measured distance difference on a staff into a horizontal and vertical distance (height) without having to perform angular computations. In the digital type the values are read directly from the displays and as such the digital tachymeter is the forebear of the (integrated) total station instrument in land surveying. Most of the instruments in my collection are from Wild Heerbrugg.