Nowadays, the automotive sector requires great quality for each product that is produced, and especially regarding those pieces or parts which need to be reliable and long lasting, and that require high properties because of their use. High temperatures, high pressures or constant friction are effects that some pieces in the engine, for example, have to endure during its working life, which is of around fifteen to seventeen years. It is precisely in the automobile’s engine where pieces suffer the most aggressive effects, and therefore, where the fabrication has to be optimized to achieve its goals. Inside the engine, with its high temperatures, great movement and extenuating friction, the piston has to find a perfect measurement in roughness in order to avoid arriving to such aggressive conditions. This is done by maintaining the oil and the fuel separated but retaining the oil to a certain level to avoid excessive friction piston-cylinder. Therefore, the study of roughness regarding fabrication of these pieces is extremely important, and in addition to this, the realization of where it can be improved and where it cannot. This paper studies a way of differentiating the various frequencies of a surface profile. First, it analyses the primary surface properties to figure out what differentiates frequencies within a sample. Then, it studies which values assigned, regarding the properties, act in a filter to differentiate frequencies. Finally, it arrives to the conclusion of what is roughness and what is waviness and their specific properties.