## 3 Results
### Frequencies of the Daily Differences between the Four Selected Methods of SD  
Figure 8 shows histograms for the daily differences among the different pairs of sunshine recorders. Generally, in all cases, the histograms resemble a normal distribution, as is indicated by the red line on the graph. Similar results were found by [PERSON] [24] and [PERSON] [15]. Figure 8: _Cont_. Table 4 shows the percentage of annual differences in daily SD among different pairs of sunshine recorders at the three synoptic stations during different time periods, based on the classification scheme proposed by [PERSON] and [PERSON] [10]. The daily differences are determined by the SD of automatic devices minus manual SD (CS). As is indicated by Table 4, approximately between 9% and 23% of all the measurements show exactly the same values (Class C1). With the exception of the CSD3_Pent and CS pair, the percentage daily differences between the automatic sensors and CS recorders fluctuate between 48% and 59% within the range of classes \(-\)C2 and C2, i.e., within the range of \(-\)0.5 to 0.5 h. Generally, the frequencies of negative differences between the automatic and manual instruments are higher than the frequencies of positive differences for the pairs at Pafos and Athalassa. The highest negative percentage was 68%, and it occurred at Pafos. In the case of Larnaca, the negative percentages of daily differences between the automatic instruments and the CS recorder range between 38% and 50%. Table 5 shows the monthly frequencies of daily differences in sunshine duration between the selected pairs of sunshine recorders in different time periods. Almost all the year around, over 50% of the differences between Gl and CS are within the classes \(-\)C2 and C2 at Larnaca. However, for the same pair at Pafos, and the same range of classes, over 50% \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Percent** & **Intervals** & \multicolumn{3}{c}{**Larnaca 2009-2012**} & \multicolumn{2}{c}{**Pafos**} & **Athalassa** \\  & & & & **2009–2012** & **2012–2015** \\ \hline
**Groups** & **Hours/Sensors** & **Gl–CS** & **CSD3\_Pent–CS** & **CSD3\_Men–CS** & **Gl–CS** & **Pr–CS** \\ \hline \(-\)**C4** & \(<\)\(-\)1.5 & 3.2 & 5.6 & 10.3 & 12.0 & 8.7 \\ \(-\)**C3** & [\(-\)1.5 to \(-\)0.5) & 15.5 & 16.5 & 18.4 & 31.8 & 28.7 \\ \(-\)**C2** & [\(-\)0.5 to \(-\)0.1) & 18.7 & 17.9 & 20.9 & 24.4 & 18.2 \\ **C1** & [\(-\)0.1 to 0.1] & 14.6 & 8.9 & 19.1 & 10.5 & 22.5 \\ **C2** & (0.1 to 0.5) & 25.6 & 12.8 & 15.6 & 13.0 & 17.3 \\ **C3** & (0.5 to 1.5) & 20.9 & 24.1 & 13.2 & 7.5 & 4.6 \\ **C4** & \(>\)1.5 & 1.5 & 14.2 & 2.6 & 0.8 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Percentages of annual differences of daily SD among different pairs of automatic devices minus CS sunshine recorders at the three synoptic stations during different time periods, based on the classification scheme proposed by [PERSON] [10]. Figure 8: Histograms of the daily differences among different pairs of sunshine recorders. The red line represents the normal distribution. of differences are recorded from September to December. Regarding the pair of CSD3_Men and CS at Larnaca (2009-2012) and the Pr and CS pair at Athalassa (2012-2015), over 50% of the differences were within the range of \(-\)C2 to C2, almost all year around.