## 3 Results
### Zephyr Wearable Sensor  
A statistically significant, strong, positive relationship was observed between the Zephyr and the ICTS, (\(\rho\) (421) = 0.524, \(p\) < 0.001). Therefore, hypothesis H2B was true. Wilcoxon signed-rank test showed that there was an agreement between the CT data recorded from the ICTS and the Zephyr, (\(Z\) = \(-\)0.661, \(p\) = 0.509). The Bland-Altman plot for comparing the CT data from both devices is shown in Figure 4a. The bias was \(-\)0.03 \({}^{\circ}\)C and the hypothesis testing was insignificant, indicating that although Zephyr read on average 0.03 \({}^{\circ}\)C less than the pill, there was agreement between the two devices. Therefore, Zephyr can be considered a good option for measuring CT. A comparison of the average temperature over time for both the Zephyr and the ICTS data is shown in Figure 4b, taking into consideration the variability and dispersion of temperature measurements among participants during the first 20 min of the study. The significant variability observed in the participants' Zephyr CT measurements, as depicted in Figure 4b, led to an investigation into the impact of individual differences on CT measurement. The results of the Mann-Whitney U test revealed a statistically significant effect of participants' past experience of working in hot conditions on Zephyr mean CT measurements (U = 0.0, \(p\) = 0.017). However, there was no significant difference in Zephyr max CT measurements (U = 2.0, \(p\) = 0.067). Participants who never avoided exercising in hot conditions had higher CT values (Mean_Zephyr CT Median = 37.39 \({}^{\circ}\)C; Max_Zephyr CT Median = 37.80 \({}^{\circ}\)C) compared to those who occasionally avoided such exercise (Mean_Zephyr CT Median = 37.26 \({}^{\circ}\)C; Max_Zephyr CT Median = 37.40 \({}^{\circ}\)C). Additionally, the Kruskal-Wallis test results demonstrated a statistically significant effect of exercise intensity on Mean_Zephyr CT measurements (\(\chi^{2}(2)\) = 5.98, \(p\) = 0.050). However, no significant effect was observed for Max_Zephyr CT measurements (Max_Zephyr CT: \(\chi^{2}(2)\) = 4.85, \(p\) = 0.089). Participants engaging in moderate-intensity exercise exhibited the highest CT measurements (Mean_Zephyr CT Median = 37.39 \({}^{\circ}\)C; Max_Zephyr CT Median = 37.80 \({}^{\circ}\)C), followed by those performing low-intensity exercise (Mean_Zephyr CT Median = 37.45 \({}^{\circ}\)C; Max_Zephyr CT Median = 37.28 \({}^{\circ}\)C), and lastly, participants engaging in vigorous-intensity exercise (Mean_Zephyr CT Median = 37.22 \({}^{\circ}\)C; Max_Zephyr CT Median = 37.22 \({}^{\circ}\)C). Furthermore, the Kruskal-Wallis test was conducted to assess the effect of participants' BMI on CT measurements, revealing no statistically significant effect (Mean_Zephyr CT: \(\chi^{2}(2)\) = 1.59, \(p\) = 0.453; Max_Zephyr CT: \(\chi^{2}(2)\) = 1.00, \(p\) = 0.606). For mean Zephyr CT measurements, healthy weight and underweight participants recorded similar CT values (Median = 37.34 \({}^{\circ}\)C), while overweight participants exhibited the lowest CT values (Median = 37.26 \({}^{\circ}\)C). In terms of Max_Zephyr CT measurements, underweight participants recorded the highest CT values (Median = 37.65 \({}^{\circ}\)C), followed by healthy weight participants (Median = 37.50 \({}^{\circ}\)C), while overweight participants had the lowest CT values (Median = 37.40 \({}^{\circ}\)C). Based on the findings of this study, there is substantial evidence to fail to reject hypothesis H2c. Similarly, the RMSE value of 0.328 showed that there is an average difference of 0.328 \({}^{\circ}\)C between the two devices. The MAE value of 0.258 indicates that the two methods of measuring CT differ by 0.258 units. However, linear regression indicated that there is a proportional bias under the distribution of data around the mean difference line (t = \(-\)18.560, \(p\) < 0.001).