## 3 Results and Discussion
### Phase 4: Evaluate the Scenarios and Determine the Measurement Error  
In this phase, a comparative analysis of the measurements made by the prototype device compared to those from the calibrated instrument was carried out. This statistical analysis of the data obtained was performed for each of the four scenarios. It consisted of capturing data every 5 min over a period of 6 h. The data obtained for the measurements in the four scenarios are shown graphically. Figure 14 shows the data for Scenario 1 (cross-ventilation). It can be observed that the data corresponding to the measurement with the prototype coincided with those of the equipment calibrated. The minimum difference between the recognized data (error) could be caused by cross-ventilation because the atmosphere was not completely steady. In addition, the CO\({}_{2}\) concentration was observed to remain at healthy levels, close to the IAQ values that can be achieved in outdoor environments. The amount exhaled by the occupant of the space had hardly any effect on the total concentration when the ventilation was cross-ventilation. Figure 15 shows the data for Scenario 2 (outdoor-ventilation). The data from the measurement with the prototype matched those of the equipment calibrated. The CO\({}_{2}\) concentration was close to health thresholds in a small range, as the window being open, the airflow renewed the amount of clean air, keeping the scene in a healthy condition for the occupant. Figure 16 shows the data for Scenario 3 (indoor-ventilation). The data from the measurement with the prototype match those of the equipment calibrated. Air renewal depends on the interior connection between the room and the rest of the building. Except for occasional measurements, the IAQ is considered to be adequate. In this case, in order to have more information, it would be necessary to perform the study of the entire building (including all the points where there could be air renewal). Figure 14: Data for Scenario 1. Figure 15: Data for Scenario 2. Figure 17 shows the data for Scenario 4 (no-ventilation). The data from the measurement with the prototype matched those of the equipment calibrated. It can be observed how the amount of CO\({}_{2}\) increased to levels considered unhealthy. After approximately 50 min, concentrations close to 1000 ppm of CO\({}_{2}\) were obtained. The instantaneous error of each measurement corresponded to the difference between the measurement obtained by the low-cost clonic device and the commercial instrument calibrated (KIMO). This measurement already incorporated the corrected measurement uncertainty of the KIMO instrument. Details of all measurements are included in the Supplementary Materials. Simultaneous measurements were obtained with both the low-cost clonic device and the instrument calibrated (KIMO), which was employed as a reference standard. As stated before, these device measurements already included both the correction and the measurement uncertainty of the KIMO instrument. The values of the mean, minimum, maximum, and standard deviation values were studied. Table 6 shows these values: \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Scenario** & **Device** & **Mean** & **Minimum** & **Maximum** &
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} \\ \hline \multirow{2}{*}{Cross-ventilation} & KIMO & 450.88 & 400 & 504 & 27.00 \\  & Prototype & 452.49 & 401 & 503 & 28.98 \\ \hline \multirow{2}{*}{Outdoor-ventilation} & KIMO & 494.07 & 405 & 585 & 51.55 \\  & Prototype & 494.45 & 407 & 582 & 50.66 \\ \hline \multirow{2}{*}{Indoor-ventilation} & KIMO & 590.57 & 402 & 734 & 79.77 \\  & Prototype & 587.39 & 408 & 741 & 89.36 \\ \hline \multirow{2}{*}{No-ventilation} & KIMO & 1087.69 & 401 & 1638 & 374.10 \\  & Prototype & 1091.24 & 420 & 1664 & 368.80 \\ \hline \hline \end{tabular} Note: The unit of measurement for CO\({}_{2}\) concentrations is ppm.  
\end{table} 
Table 6: Comparative study of the sample with KIMO and prototype measurements. Figure 16: Data for Scenario 3. Figure 17: Data for Scenario 4.