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Most currently available systems need to set the measuring system directly on the soil sample to be tested, which can disrupt the soil and therefore the results (Cole 1978, Clayton et al. 1989). Thus, some authors have implemented contactless systems, including devices based on the use of a  laser spot (eg Romero 1999; Dasari 2002; Messerklinger & Springmann 2007). These devices have the advantage of not requiring contact with the specimen and so do not disrupt the mechanical behaviour of soil.