## 2 Materials and Methods
### Apparatus Description  
In this subsection, a comprehensive description will be provided for each of the devices and sensors utilized in the apparatus. While some sensors were already incorporated into the devices, we additionally included additional sensors to acquire the necessary data. Figure 1 illustrates the proposed apparatus, including all the employed devices and sensors. All devices are networked and communicate via the use of wireless networking (Wi-Fi) and Bluetooth communication standards. Custom applications for the Android and Tizen operating systems have been developed to facilitate device synchronization, ensuring accurate data collection. The system exhibits a great degree of customization, allowing the researcher the flexibility to choose various settings. For instance, it enables the user to choose the quantity and type of collected data (signature, sentences, words, and letters). Using a configuration file, it is possible to specify particular phrases and/or terms to be collected. Managing the acquired data may be accomplished with ease, including tasks such as transferring it to a remote computer or removing it from the present device. In addition, the calibration of the magnetometer is performed automatically before the commencement of data collection. The primary component of our proposed apparatus was an Android tablet. The device model in question is a Samsung Galaxy Tab S6. As reported by GSMArena [30], the tablet in question has a screen size of 10.5 inches and exhibits a resolution of 1600 by 2560 pixels. It is equipped with a Qualcomm Snapdragon 855 system-on-chip and 6 GB of RAM. The tablet is initially shipped with the Android Pie operating system with the One UI 1.5 user interface. At the time of writing, the latest software version available for update is Android 12L, which is accompanied by One UI 4.1.1. Nonetheless, we decided to postpone the upgrade and maintain the system's original version. The device is equipped with a stylus referred to as \(S\)_Pen_. It serves the purpose of capturing pressure data when engaging in handwriting activities. The stylus has a sensitivity range of 4096 distinct levels depending on the amount of pressure applied. However, regrettably, the stylus has several drawbacks that are important for our research. Based on a response obtained from the official Samsung Developers forum [31], it has been indicated that the S Pen Remote Software Development Kit (SDK) does not include functionality for capturing stylus pressure levels or stylus tilt data. However, despite the constraints imposed by the official SDK, the data for stylus pressure levels may still be acquired using the MotionEvent object. Multiple sensors are built into the tablet, one of which holds particular importance for our research. Specifically, during the signing process, data were obtained from the magnetometer (compass). To gain insight into the integrated sensors, three specific applications were employed: Sensors Toolbox [32], Sensors Multitool [33], and Device Info: Phone CPU, System [34]. Based on the aforementioned Android applications, the Galaxy Tab S6 is equipped with the AK09918 3-axis electronic compass. As per the official datasheet from the Asahi Kasei Microdevices Corporation website [35], the AK09918 integrated circuit (IC) provides a 16-bit data output for each three-axis magnetic component. The magnetometer has a 0.15 \(\upmu\)T/LSB measuring sensitivity with a maximum range of 4192 \(\upmu\)T. The holder that was custom-made utilizing 3D printing is used for attaching small magnets to the S Pen. Their goal is to generate a changing magnetic field during writing to obtain a unique trace of each user's handwriting. Figure 2 depicts custom-made holders utilized in the proposed apparatus. In addition, a customized ring made using a 3D printer is employed to disrupt the magnetometer's readings of the magnetic field. It functions as a holder, facilitating the positioning of tiny magnets on its upper surface.