Refining the classical distinction between fixed and circulating capital in "Das Kapital", Karl Marx emphasizes that the distinction is really purely relative, i.e. it refers only to the comparative rotation speeds (turnover time) of different types of physical capital assets. Fixed capital also "circulates", except that the circulation time is much longer, because a fixed asset may be held for 5, 10 or 20 years before it has yielded its value and is discarded for its salvage value. A fixed asset may also be resold and re-used, which often happens with vehicles and planes.