## 3 Materials and Methods
### Hardware and Software Layer  
In order to verify the assumptions of the system model concept, tests were carried out to check, in particular, the correctness of the choice of the measurement of the EEG signal emitted by the operator's brain in order to identify his/her level of concentration. In our study, we utilized the MindWave Mobile device 1, coming from NeuroSky (San Jose, CA, USA) [18]. We intended to verify whether the single-electrode EEG signal measurement is sufficient to monitor the concentration level of the operator of machinery and equipment.  
The MindWave Mobile is equipped with a single, dry frontal electrode named Fp1 (according to the international 10-20 standard defining electrode placement points during EEG signal analysis) and an ear-mounted reference clip.  
NeuroSky's product is powered by a single AAA battery, which provides between 6 and 8 h of continuous operation. The data transmission rate realized by the device is equal to 250 kbit/s. The device operates in the frequency range of 2.420-2.471 GHz. The maximum signal strength is equal to 6 dBm. The sampling frequency for measurements carried out using the NeuroSky MindWave Mobile is set to 512 Hz [6].  
In addition to the raw EEG signal, the device transmits the level of focus (attention) and relaxation (meditation). Both ratios are dimensionless. The manufacturers of the equipment do not provide details of their determination, only information on their correlation with alpha, beta and theta waves are given [19].  
For the purpose of this study, a custom-build software was developed to record the data, i.e., time, focus and meditation level, and save the data for further analysis. The software is compatible with any kind of device running the Android operating system. It contains summation filters that process the data from the data logger and correlate it according to the time base with the events that were gathered by the video recorder.  
Figure 2 shows the block diagram of the test bed for the operator's concentration measurement system. The testbed was equipped with an EEG measurement tool, namely the MindWave Mobile device, from which data were recorded in a data logger, which is a mobile application running on a mobile Android-powered terminal. The workstation also consisted of a video recorder, which allowed the measurement results to be correlated with specific recorded events, namely visual information. It should be noted that all devices were synchronized in time.  
Tests were carried out for two variants of machine operators: car drivers and people performing simple manual tasks. Drivers of passenger cars consisted of o groups: people who have a driving license for more than 10 years, and people who have a driving license for less than 1 year. People performing precise manual activities were assemblers of SMD electronic components with 10 years of experience.  
During our study, the following system functions were verified:  
* Whether the system is able to identify the response to specific stimuli while driving (short-distance driving).
* Whether the system can identify measurement differences (driving two drivers on the same route with different driving skills).
* Whether it is possible to identify distractions over short and long periods of time (long-distance driving and simple manual tasks).  
During the field tests, the following parameters were recorded and monitored: time, level of concentration and level of meditation (relaxation).