## 1 Introduction  
Surfaces--the outermost layer of any workpiece--are created after, i.e., machining. The texture of the surface affects many properties of machine elements, such as contact mechanics, sealing, friction, and wear [1]. Surface topography is formed during the last stages of the machining treatment. Some properties, such as material contact, sealing, friction, lubricant retention, and wear resistance, are related to surface topography. Taking the above into consideration, inter-operational control during machining is a must to obtain the desired form and values of surface irregularities. Characterization of these surface irregularities is obtained by a number of measurement methods that examine the surface from different points of view and provide different information. Typically, there are three measuring techniques that can be divided into two types according to the results: quantitative and visualization. There are contact measurements, optical measurements, and other technical solutions, including atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM, scatterometry) [2; 3; 4]. There are two main measuring methods in the industrial environment, contact and optical, with the undoubtedly dominant role of contact profilometry. Contact surface profilometers make physical contact with a measured specimen using a sensitive stylus, which is drawn across the component surface. This can register surface deformations and variations as fluctuations in friction and applied resistance. It is suitable for roughness, waviness, and form measurements and is impervious to optical interference and lubricating elements. In engineering, one of the problems is that environmental conditions can vary widely between the machine shop and the inspection room. This is where the stylus method scores over other methods. The fact that the stylus touches the surface can be an advantage in two ways. The first is that the stylus can push aside debris and penetrate films that would otherwise mask the geometry. The second is that the stylus can be used to act upon the surface, as in the case of the scanning microscopes, to initiate discharge, disrupt fields, and behave in a proactive way as required [5; 6; 7].  
Surface preparation for roughness measurements is often an omitted issue both during an experiment and in everyday metrology practice. [PERSON] and [PERSON] stated [7], \"a surface is clean when any residual contamination fails to affect the functionality of that surface\". In terms of roughness measurements, it may be changed to: any residual contamination fails to affect changes in the obtained results with assumed accuracy.  
In [8], the author states: \"From the point of view of engineering metrology, there is usually not much time to prepare a specimen workpiece prior to measurement. All that can be attempted in in-process measurement is a contact wiper on the surface or a brush for internal holes. Sometimes, compressed air is used to clear the surface of debris and oil films [...]\". Practically, the most common approach to cleaning surfaces before roughness measurements is cleaning through the blowing of compressed air against the surface. The other common methods include cleaning with a dust-free cloth or a cloth soaked in isopropyl alcohol or acetone; less commonly, sampling can occur after bathing in a cleaning liquid. Guides usually give a brief description of how to prepare the specimen for the measurement, e.g., \"Before performing a measurement it is important to remove any oil, grease, dust or mist from the surface [...]\" [9; 10]. Many authors also include a short sentence such as \"sample after cleaning/preparation\" or even without any information about such preparation [11; 12; 13; 14; 15; 16]. The absence of such information is not a big mistake (although it is good engineering practice to include it), but inaccurate or completely incorrect surface preparation for measurement results in erroneous measurement results.