## 3 Results and Discussion  
A total of 25,000 measurements were gathered over a period of 3 months, from 5 September to 5 December 2024, in the central part of Athens, Greece. The testing revealed that all five modules exhibit a small deviation on the computed values, which can prove to be important in determining the accuracy class of the device. As mentioned before, the electromechanical meter can measure the real power only, while the microvip3 and the multimeter DMTME calculate the incoming reactive power without identifying whether it is inductive or capacitive with respect to the load specification. The last two instruments offer a wide variety of measurements for better information. For ease of identifying the values monitored, certain IDs were used, including  
* A+: stands for real power (Module Value 1.8.0);
* Q+ is identified as reactive power through an inductive load (Module Value 3.8.0);
* Q\(-\) is established as reactive power through a capacitive load (Module Value 4.8.0). The MM200 and the smart MK10A have similar results, with the EDMI model showing slightly higher values, as smart devices have more accuracy compared to old electromechanical meters [15]. Zennio has less accuracy, but that is considered as typical, since it is not a typical smart meter, such as the widely used Mk10A. Similarly, the Microvip and Dmtme modules are validation tools used mainly for monitoring purposes; hence, they are not appraised as meters, as their precision in constant metering is lower, as shown in Figure 10.  
Measurements for real power, which is available for all meters, are summarized in Table 2.  
Figure 10: Real power measurements by the five distinct devices for accuracy comparison. Figure 9: Zennio KES Plus layout: (a) the installation on the control panel with the power supply and module for additional ports; (b) user interface configuration menu. In the next step, positive reactive power, caused by an inductive motor, is measured. The electromechanical meter cannot measure this type of power, so values are not available. The other four modules can efficiently compute the inductive reactive power, with the Mk10A, Microvig 3 and Zennio appearing to have almost identical values, with small fluctuations, which are depicted in Figure 11.  
The ABB model is presenting increased accuracy and complies with the specifications of the manufacturer [25]; thus, it is ideal for industrial use, where precision in measuring reactive power is essential, as it can save costs for both the consumer and the energy supplier. All values for the Q+ reactive power are outlined in Table 3. \begin{table}
\begin{tabular}{c c c c c c} \hline
**A/A** & **Landis\&Gyr** & **EDMI** & **ELControl** & **ABB** & **Zennio** \\  & **MM2000** & **Mk10A** & **Microvig3** & **DMTME** & **KES-Plus** \\ \hline
1 & 0 & 0 & 0 & 0 & 0 \\
2 & 70.60 * & 71.00 & 45.00 & 60.20 & 69.00 \\
3 & 206.70 & 208.50 & 123.50 & 177.20 & 208 \\ \hline
4 & 371.40 & 364.60 & 273.00 & 312.70 & 355.00 \\
5 & 507.20 & 511.95 & 382.80 & 436.30 & 497.00 \\ \hline
6 & 680.90 & 684.90 & 534.80 & 580.50 & 663.00 \\
7 & 821.30 & 828.00 & 623.20 & 687.70 & 798.00 \\
8 & 908.30 & 914.10 & 702.00 & 755.20 & 887.00 \\
9 & 953.90 & 960.00 & 742.30 & 792.20 & 914.00 \\ \hline
10 & 1000.40 & 1006.75 & 783.25 & 830.10 & 959.00 \\
11 & 1071.70 & 1081.40 & 838.10 & 888.60 & 1032.00 \\
12 & 1150.20 & 1157.30 & 954.45 & 953.70 & 1106.00 \\
13 & 1229.70 & 1237.40 & 1057.20 & 1020.00 & 1184.00 \\
14 & 1280.80 & 1288.70 & 1104.10 & 1061.30 & 1233.00 \\
15 & 1352.80 & 1360.90 & 1206.70 & 1122.00 & 1304.00 \\
16 & 1401.40 & 1409.75 & 1247.20 & 1160.70 & 1351.00 \\ \hline \end{tabular}  
* All values are in KWh.  
\end{table} 
Table 2: Total real power consumption (A+) in kilowatt-hours for each meter. Figure 11: Positive reactive power (Q+) comparison for the 4 available modules. In this section, the computation of negative reactive power, or capacitive power, is presented.