# Computer Vision-Based Approach for Reading Analog Multimeter
## 5 Results and Discussions
### Further Results and Discussion

Table 8: Results of using the A-meter YF-370A with function select (a) “\(\Omega\times 10\)” to measure the resistance of the 50 \(\Omega\) resistor, (b) “\(\Omega\times 10\)” to measure the resistance of the 220 \(\Omega\) resistor, (c) “\(\Omega\times 10\)” to measure the resistance of the 1 K\(\Omega\) resistor, (d) “\(\Omega\times 1\)” to measure the resistance of the 1 K\(\Omega\) resistor, and (e) “\(\Omega\times 10\) K” to measure the resistance of the 70 K\(\Omega\)The performance evaluations of those experiments presented previously were based on inspection by the human eye (\(V_{h}\)), where looking at the A-meter (or viewing angle) will result in an error due to reading the value indicated by the pointer. Similarly, such a situation (like the \"tilted surface\" noted in the previous experiments) will also appear in our computer vision-based approach. Hence, it can be concluded that the errors resulting from the A-meter itself and the observation from human eyes or a vision sensor are inevitable under the scenario of using an A-meter. In order to further confirm the feasibility of the proposed method, a digital multimeter (model DMM-85) instead of human eyes was used to read the value of measurement as ground truth (\(V_{dm}\)). By replacing \(V_{h}\) by \(V_{dm}\), Equation (24) was also used for the accuracy evaluation. Table 10 reports that a mean accuracy of 95.61% can be achieved. Note here that the _little-change-large-multiplier effect_ appears in the experiment of the last row of Table 10, where the accuracy decayed to 88.77%. To investigate the influences of translation and/or rotation using our approach, we experimented with shifting and/or rotating the camera of our system to read the A-meter. The tester calibrator (model AOIP CMU 310) was used to provide a stable 24 Vdc as the ground truth and the function of the A-meter was switched to \"DC 50V\" for the experiments. Six scenarios were designated as the A-meter in the captured image: (1) shifted right, (2) rotated right, (3) shifted right and rotated left, (4) shifted left, (5) rotated left, and (6) shifted left and rotated right, where scenarios (2) and (5) were obtained by the arrangements shown in Figure 16a,b, and their illustrative results are presented in Figures 17 and 18, respectively. In this experiment, there were 100 consecutive runs for each scenario in our approach. The measured DC voltages for the six scenarios are plotted in Figure 19, and their statistical results are reported in Table 11. The plots shown in Figure 19, demonstrate that a slight fluctuation existed when reading the A-meter using our computer vision-based system. In addition, as reported in Table 11, when \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{Rotation_{A\text{-}meter}}\) & \(\mathbf{I}\) & **Measurement Target** & \(\mathbf{V_{dm}}\) & \(\mathbf{FS_{p}}\) & \(\mathbf{V_{p}}\) & _Accuracy (\%)_ \\ \hline \(12^{\circ}\) & 31.7 & 5 Vdc adaptor & 5.36 Vdc & DCV 10 & 5.239 Vdc & 97.74\% \\ \(-25^{\circ}\) & 16.6 & 7.5 Vdc adaptor & 8.06 Vdc & DCV 10 & 7.676 Vdc & 95.24\% \\ \(18^{\circ}\) & 128 & 110 Vac line power & 113.6 Vac & ACV 250 & 113.244 Vac & 99.69\% \\ \(19^{\circ}\) & 127.3 & 220 Vac line power & 227 Vac & ACV 250 & 227.56 Vac & 99.75\% \\ \(0^{\circ}\) & 67.7 & DC current \({}^{*}\) & 7.53 mA & DCmA 25 & 6.943 mA & 92.20\% \\ \(9^{\circ}\) & 126.8 & 470 \(\Omega\)\({}^{\dagger}\) & 469 \(\Omega\) & \(\Omega\times 10\) & 488.4 \(\Omega\) & 95.86\% \\ \(-17^{\circ}\) & 74.8 & 10 K\(\Omega\)\({}^{\dagger}\) & 9.97 K\(\Omega\) & \(\Omega\times 1\)K & 11.09 K\(\Omega\) & 88.77\% \\ \hline \hline \end{tabular}  
* 1.5 Vdc battery; \({}^{\dagger}\) Resistance provided by the DC resistance controller ZX99A [20].  
\end{table} 
Table 10: Results of comparing the measurements (\(V_{dm}\)) with a digital multimeter (model DMM-85) to those (\(V_{p}\)) with the A-meter YF-370A read by the proposed method. The mean accuracy was 95.61%.