## 4 Results
### Inventory Related Costs
#### 4.1.5 Total Inventory-Related Costs  
Minimal \(\mathrm{C_{TOT}}\) on a level of individual SE in a 7-day WS occurs for R = 10 and LT = 10, with a value of 4404.84 EUR/year. Minimal \(\mathrm{C_{TOT}}\) on a level of individual SE in a 5-day WS occurs for R = 2 and LT = 13, with a value of 4457.79 EUR/year. Maximal \(\mathrm{C_{TOT}}\) on a level of individual SE in a 7-day WS occurs for R = 1 and LT = 0, with a value of 24505.89 EUR/year. In a 5-day WS, maximal values are observed for identical operating conditions with an 18881.77 EUR/year value. Analyzing average values of \(\mathrm{C_{TOT}}\) per R and LT groups separately, maximal average \(\mathrm{C_{TOT}}\) in a 7-day WS occurs for the R = 1, LT = 0 (R + LT = 1) group of SEs, with a value of 24236.88 EUR/year and minimal 4684.02 EUR/year for R = 15 and LT = 5. Maximal average \(\mathrm{C_{TOT}}\) in a 5-day WS occurs for the same group R = 1, LT = 0 (R + LT = 1) of SEs, with a value of 18388.12 EUR/year and minimal 4702.37 EUR/year for R = 14 and LT = 0 (R + LT = 14). Values of average \(\mathrm{C_{TOT}}\) per R and LT groups for an FR of 99.9% within five and 7-day WSs and for high and low demand variability are visible in Figure 10.  
Figure 9: (**a**) Reduction in \(\mathrm{C_{H}}\) for FR 99.9% per R + LT group for a 7-day compared to 5-day WS. (**b**) Increase in average \(\mathrm{C_{H}}\) per R + LT group and WS for an FR 99.9% and SD 30 compared to FR 89.9%. When analyzing C\({}_{\text{TOT}}\) per R + LT group, we can conclude that maximal average C\({}_{\text{TOT}}\) occurs in the R + LT = 1 group regardless of the WS and demand variability, as visible in Figure 11 for high demand variability. Minimal average C\({}_{\text{TOT}}\) occurs in different R + LT groups, emphasizing the need for simulation modeling in periodic review inventory systems with stochastic market demand. Table 3 shows the average C\({}_{\text{TOT}}\) for R + LT groups for both WS and demand variabilities, along with their components. Figure 10: (a) C\({}_{\text{TOT}}\) per R and LT groups for FR 99.9 in a 5-day WS for high demand variability. (b) C\({}_{\text{TOT}}\) per R and LT groups for FR 99.9 in a 7-day WS for high demand variability. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c c} \multicolumn{11}{c}{**5-Day WS**} & \multicolumn{1}{c}{**7-Day WS**} \\ \multicolumn{11}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 10**} & \multicolumn{1}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 10**} & \multicolumn{1}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 30**} & \multicolumn{1}{c}{**SD 40**} & \multicolumn{1}{c}{**SD 50**} & \multicolumn{1}{c}{**Cp**} & \multicolumn{1}{c}{**Cr0T**} & \multicolumn{1}{c}{**Ca**} & \multicolumnFor a 5-day WS, the minimal average C\({}_{\text{TOT}}\) is observed in the R + LT = 16 group with values of 4779.54 EUR/year for SD 10 and 5002.31 EUR/year for SD 30. The maximal average C\({}_{\text{TOT}}\) in the same WSs is 18710.71 EUR/year for SD 10 and 18065.53 EUR/year for SD 30. For a 7-day WS, the minimal average C\({}_{\text{TOT}}\) of 4646.16 EUR/year occurs in the R + LT = 22 group for SD 10, while for SD 30, it is 4949.85 EUR/year. The maximal average C\({}_{\text{TOT}}\) in the same WSs is 24409.15 EUR/year for SD 10 and 24064.61 EUR/year EUR for SD 30. On average, C\({}_{\text{TOT}}\) is 3.5% higher for high demand variability within a 5-day WS and 4.7% for a 7-day WS. With increased R + LT value, the relative difference in C\({}_{\text{TOT}}\) due to increased demand variability increases within the same WS with minor exceptions. Due to the change in the R + LT group from minimal to maximal values, C\({}_{\text{TOT}}\) can be reduced 3.8 times in a 5-day and 5.1 times in a 7-day WS, i.e., a company can reduce costs, according to our SC and periodic review (R, s, S) inventory model, about 13500.00 EUR/year in a 5-day and 19440.00 EUR/year in a 7-day WS while satisfying same percentage of market demand.