Roller compaction is the laboratory method that most closely simulates on-site compaction. The machine can be configured to operate with a single or twin wheels depending on the mould size. The wheels track the surface in overlapping wheel-paths using sequences specified in EN 12697-33 or custom sequences designed by the user. The base of the mould is incrementally raised by a precision jacking system and the system is tracked to keep it level with the top of the mould. Compacted slabs can be from 50 to 150mm thick. 500 x 180mm slabs are usually wheel tracked in the Cooper Technology Large Wheel Tracker, whilst 600 x 400mm slabs are normally cut to produce trapezoidal or prismatic specimens for fatigue, modulus tests and Duriez test.