## 2 Materials and Methods
### Experimental Procedures  
To validate the effectiveness and reliability of the developed armlet with a wet circuit system in accurately measuring the wet circuit in closed channels, an experimental procedure was conducted. The aim of this procedure was to assess the strap's performance under controlled conditions and determine its practical suitability. In this article, we will provide a detailed exploration of the experimental process, highlighting the key steps and considerations involved. The experimental setup commenced with the careful selection of a test channel that closely resembled the dimensions of the target closed channels (Figure S2). The material and geometry of the test channel were meticulously chosen to accurately replicate real-world conditions. Subsequently, the armlet with a wet circuit measurement system was securely installed within the test channel, following the recommended guidelines provided by the development team. The strap's width, attachment of measurement electrodes, and any necessary fastening mechanisms were implemented in accordance with the design specifications (Figure S3). Prior to proceeding with the experiments, the armlet with a wet circuit measurement system underwent calibration using a reference standard or known flow rates. This calibration step was crucial in ensuring the accuracy and consistency of subsequent measurements.  
The experimental procedure involved introducing controlled variations in the flow rate of water or sewage to assess the measurement strap's capability in accurately measuring the wet circuit. These variations simulated different flow conditions typically encountered in closed channels, including low-flow periods, peak flow events, and transitional flow states. Throughout the experiments, continuous data collection took place from the measurement strap's sensors or electrodes. These sensors captured essential parameters such as flow rate, water level, and other variables of interest. The data acquisition system employed was capable of capturing high-resolution measurements at predefined intervals. The collected data from the armlet with wet circuit measurement system were then subjected to comparative analysis, wherein they were compared against reference measurements or established standards. Statistical analyses, including error calculations, and correlation assessments, were conducted to evaluate the strap's accuracy, precision, and reliability in measuring the wet circuit. Based on the comparative analysis, the performance of the measurement strap was comprehensively evaluated, taking into account factors such as measurement accuracy, sensitivity to flow variations, response time, and robustness against environmental factors. These evaluations aimed to determine the strap's suitability for practical use in closed channels (Figure S4). By conducting this rigorous experimental procedure and thoroughly evaluating the performance of the armlet with a wet circuit measurement system, we obtained valuable insights into its effectiveness and reliability in monitoring the wet circuit in closed channels. These findings contribute to advancements in measuring technology, providing more accurate and reliable solutions for monitoring closed channels in real-world scenarios.