# Computer Vision-Based Approach for Reading Analog Multimeter
## 5 Results and Discussions
### Further Results and Discussion
\begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{I}\) & \(\mathbf{V_{h}}\) **(Vac)** & \(\mathbf{V_{p}}\) **(Vac)** & _Accuracy (\%)_ \\ \hline \(133.6\) & 109 & 111.039 & 98.14\% \\ \(129.5\) & 110 & 113.439 & 96.87\% \\ \(123.1\) & 109 & 111.419 & 97.78\% \\ \(95.3\) & 109 & 110.226 & 98.88\% \\ \(54.0\) & 107.5 & 111.742 & 96.05\% \\ \(48.3\) & 109.5 & 113.448 & 96.39\% \\ \(40.7\) & 108 & 112.083 & 96.22\% \\ \(36.7\) & 110 & 112.111 & 98.08\% \\ \(23.0\) & 107.5 & 112.083 & 95.74\% \\ \(8.1\) & 110 & 114.130 & 96.25\% \\ \(7.5\) & Difficult to read & 113.107 & NA \\ \(6.0\) & Difficult to read & Fail to locate \(\mathbf{R}_{IM}\) & NA \\ \(5.8\) & Difficult to read & Fail to locate \(\mathbf{R}_{IM}\) & NA \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Results of reading the A-meter YF-370A with 15.425\({}^{\circ}\) rotation for the measurement of the 110 Vac line power under variant illumination. the camera was located at the left-side relative to the A-meter (e.g., scenarios (1)-(3)), the reading value was higher than 24 Vdc, and vice versa (e.g., scenarios (4)-(6)). This matches with the relationship among the observer, needle, and scale along a line of sight. Note here that the lowest value (0) of the \"DC 50V\" scale on the A-meter was located at the left-end, whereas the highest value (50) was located at the right-end (see Figures 17 and 18 for reference).Even though the recognition value produced by our system was not always as stable as the digital value displayed in the tester calibrator, a mean accuracy of around 98% was still able to be achieved. As a short conclusion, an \"uncertainty problem\" exists when obtaining measurement values from an analog meter. Two obvious uncertainties can be observed during the measuring process. First, since the measurement value is indicated by rotating a needle-type pointer onto a marked scale, an error will result from the mechanical rotation, the quality of the pointer, and the scale. Secondly, viewing directly onto the meter by not only the human eye or a camera will also lead to a reading error as the experimental results showed. Because the location of the ROIs in our approach was based on template matching, as presented in Section 2.3, the fundamental templates needed to be trained and built in prior. Even though the adopted templates are fixed and limited in the current system, based on the previous experiment, it was determined that it was worth conducting another experiment to examine the rough effective range. Again, the tester calibrator (model AOIP CMU 310) was used to provide a stable 24 Vdc as ground truth and the function of A-meter was switched to \"DCV 50\" for experiments. We moved the camera to read the A-meter and examine the effective result repeatedly. Finally, an effective range, as drawn in Figure 20, was obtained, namely, it was determined that the camera should be placed at a location about 13\(\sim\)15 cm distance from the A-meter and the viewing orientation should be within \([-18^{\circ},+18^{\circ}]\) about the center line. Note here that F has a distance from the A-meter of 16 cm; in this case, our system still can function well. The statistical results reported in Table 12 confirm that our computer vision-based approach can allow the A-meter to be read within the effective range drawn in Figure 20. If the camera is placed outside the effective region, reading the A-meter will fail. For example, consider the H and I in Figure 20. H and I have distances of 12 cm and 17 cm from the A-meter, respectively, and represent the camera being placed outside the effective range. Their experimental results displayed in Figures 21 and 22, respectively show that they fail to read the A-meter. As a comment, the scalability of the current system will depend on the A-meter included in the processed image, the resolution of the image, as well as the set of templates to be trained.