## 3 Results  
Table 1 displays the temperature for every fixed condition (fixed temperature inside the fridges, room and furnaces described in Section 2.2) during the laboratory experiment, measured by the external temperature sensor, including the mean and standard deviations. The external sensor was placed 20 cm away from the fruit in all cases.  
According to the scatterplot in Figure 5a the pairs of the measurements do not seem to deviate more than 0.5 units from the identity line. This is interpreted as minor differences among the core and surface temperatures especially for temperatures ranging from 9 \({}^{\circ}\)C to 19 \({}^{\circ}\)C. In Figure 5b the Bland-Altman and Limits of Agreement (LOA) plot is displayed [43; 44; 45], which were generated using the 'MethodCompare' package in R version 4.0.2 (The R Foundation for Statistical Computing, Vienna, Austria). The limits of agreement in the plot (blue dashed lines and a solid line for the regression) indicate that there is a positive bias of the measurement method for low temperature values and a negative bias for high values. The linear trend of the Bland-Altman plot indicates possible correlation between differences and averages, and difference in precision of the methods which is confirmed in the precision plot (Figure 6b). There were no outliers detected.  
After the analysis, the results revealed a differential bias of 0.331 (95% CI: 0.299, 0.363) and a proportional bias of 0.982 (95% CI: 0.981, 0.983). The bias is positive for low values and negative for high values. Table 2 summarizes the biases with their corresponding 95% confidence intervals. The differential bias is a constant that the method adds to its measurements regardless of the true value being measured as per [PERSON] [39]. The proportional bias is the amount of change observed by the method if the true value changes by one unit [43]. The Bland-Altman LOA plot on the other hand estimates a differential bias of 0.958 (95%CI: 0.658, 1.28) and a proportional bias of 0.976 (95%CI: 0.958, 0989) revealing the inadequacy of the specific method since it only assesses the variability of the differences but not each method separately.  
The bias is displayed in Figure 6a and decreases as the true values increase until it reaches 0 at around 19 degrees of Celsius then increases at the opposite direction. Specifically, almost a zero bias was found around 19 \({}^{\circ}\)C, \(-0.2\)\({}^{\circ}\)C at 30 \({}^{\circ}\)C and almost \(-0.4\)\({}^{\circ}\)C at 40 \({}^{\circ}\)C. According to our results for a temperature of 40 \({}^{\circ}\)C in the core, the surface sensor will measure 39.612 (0.331 + 0.982*40), which gives a total bias of \(-0.4\)\({}^{\circ}\)C compared to the core. The precision of each sensor is displayed in Figure 6b indicating that the core measurements are more precise than the surface temperatures revealing fluctuations of maximum 0.1 \({}^{\circ}\)C on absolute value when the surface temperature is measured and a  
Figure 4: (**a**) The proposed device set during the field experiment. (**b**) The proposed device set in the Elvem CLP 600 chamber during the laboratory experiment.  
constant difference of precision between the core and the surface of 0.2 \({}^{\circ}\)C with the core being more precise. This indicates that the core retains the temperature for more time than the surface much more in lower temperatures rather than in higher.