Complex sentence: In the 1870s he invented a pocket cephalometer, or as he called it, a "Compass of Coordinates", which was an instrument that allowed one to quickly measure the head's various angles, diameters, and profiles.
Split into simpler sentences: In the 1870s he invented a pocket cephalometer, or as he called it, a "Compass of Coordinates". An instrument which allowed one to quickly measure the head's various angles, diameters, and profiles.