## 2 Materials and Methods
The measuring arm is equipped with a rigid straight Renishaw probe for Faro. The device's indication inaccuracy is \(\pm\)0.071 mm throughout the entire measuring range. The FARO Cam2 MEASURE 10.4 software is used to operate the device. Operating a measuring arm requires the continuous involvement of a trained operator. The rigid measuring probe necessitates manually sending a pulse to confirm its contact with the measured element. The measuring arm is a device with a significant measurement error, but it allows for the rapid movement of the probe over the measured element, which significantly speeds up the measurement process. The measuring process involves manually moving the arm, which can be quite exhausting during long measurements and may negatively affect the measurement result. The third measurement was conducted using the manual measuring machine MITUY-OYO FJ-805 (Nakatsugawa, Japan)--Figure 2.  
This is a bridge-type machine. Its mode of operation requires the involvement of an operator who moves the machine using a control panel. The direction of the joystick levers' displacement corresponds to the direction of the machine's support movement. Figure 2: Manual measuring machine MITUTOYO FJ 805 [Photography by [PERSON]]. Two joysticks are used for control--one for moving on the X and Y axes, the other in the direction of the Z-axis [20]. This machine is equipped with a RENISHAW PH 10 M (Gloucestershire, UK) measuring head and a PT7M measuring probe (Gloucestershire, UK). The probe type is discrete. The measuring element is a ruby ball with a diameter of 3 mm. The axial inaccuracy of the machine's indication is U95 = (4 + 0.5 L/100) \(\upmu\)m, the value L is the measured length expressed in millimeters, and 0.5 L is half of this value. The Geopak-3 software, version 5.34 (PL), is used to operate the device. Measurement with a manual machine is time-consuming and requires the participation of moderately skilled personnel. Approaching the measurement points is performed manually, with the operator deciding the point of contact between the probe and the element. The movement to the respective measurement points of the element occurs at a low speed. The advantage of this machine is its design. Air bearings do not cause wear on the machine's moving parts. The measuring head used in it is a precise device, and the transmission of the signal to the machine's controllers occurs automatically upon the probe's contact with the surface being processed. In order to standardize the results, the plate was initially based. A grid was also applied to facilitate the approach to selected points during measurements with the arm. The approach in the manual machine was based on the display of the measuring probe position. The data obtained using the CMM machine are subject to a small measurement error; hence, the measurement using this machine was chosen as the reference. By comparing the time needed to conduct the study with the obtained result, a comparison of the achieved examination accuracy to the time required for its execution was made for the three evaluated methods. As the final result of the study time, we consider the time of preparing the measurement station, including writing a program for the CMM machine, and the time needed to collect the designated number of points from the studied surface. The least squares method was used to determine the parameters describing the plane based on the data from the obtained point cloud. The article presents examples of tests in real conditions that we often encounter during repairs and maintenance of industrial equipment. Results for industrial conditions were achieved, which was crucial for this study, and an anomaly was indicated for the error detected by the measuring arm. Figure 3 illustrates the process of surface flatness testing, organized in a hierarchical and logical manner. It begins with problem analysis, including the definition of flatness and its significance in construction.