## 4 Results
### Inventory Related Costs
#### 4.1.3 Holding Cost  
Inventory holding costs are proportional to the lowest AIL required to fulfill the FR under the working conditions calculated for each SE. On a level of individual SE, minimal C\({}_{\rm H}\) occurs for R = 1 and LT = 0, with a value of 122.36 EUR/year in a 7-day and 355.99 in a 5-day WS. Maximal C\({}_{\rm H}\) on a level of individual SE in a 7-day WS occurs for R = 15 and LT = 15 (R + LT = 30), with a 4006.84 EUR/year value. In a 5-day WS, maximal values are observed for R = 11 and LT = 15 (R + LT = 26) with a cost of 4324.55 EUR/year. When analyzing average values of C\({}_{\rm H}\) per R and LT groups separately, maximal average C\({}_{\rm H}\) in a 7-day WS occurs for the R = 15, LT = 15 (R + LT = 30) group of SEs, with a value of 3236.34 EUR/year and minimal 173.28 EUR/year for R = 1 and LT = 0 (R + LT = 1). Maximal average C\({}_{\rm H}\) in a 5-day WS occurs for the group R = 11, LT = 15 (R + LT = 26) of SEs, with a value of 3893.73 EUR/year and minimal 439.70 EUR/year for R = 1 and LT = 0. Generally, the average C\({}_{\rm H}\) increases with the increase in R + LT, as visible in Figure 8. When analyzing average values of C\({}_{\rm H}\) per R + LT groups, we can conclude that minimal C\({}_{\rm H}\) occurs in R + LT = 1 and maximal in R + LT = 30, regardless of the WS and demand variability. For a 5-day WS, the minimal average C\({}_{\rm H}\) for SD 10 is 374.61 EUR/year, while for SD 30, they are 34.7% higher, i.e., 504.79 EUR/year. The maximal average C\({}_{\rm H}\) in the same WSs is noticed for R + LT = 30, with values of 3335.90 EUR/year for low demand variability and 3592.70 EUR/year for high demand variability. For a 7-day WS, the minimal average C\({}_{\rm H}\) for SD 10 is 131.12 EUR/year, while for SD 30, with 215.45 EUR/year, it is 64.3% higher compared to SD 10. The maximal average C\({}_{\rm H}\) in the same WSs is noticed for R + LT = 30, with values of 3077.72 EUR/year for SD 10 and 3394.95 EUR/year for SD 30. Figure 7: (**a**) Increase in average C\({}_{\rm T}\) for FR 99.9% per R + LT group for a 7-day compared to 5-day WS. (**b**) Change in average C\({}_{\rm T}\) per R + LT group and WS for an FR 99.9% and SD 30 compared to FR 89.9%. The impact of the R + LT group changing from minimal to maximal values of average \(\mathrm{C_{H}}\) is from 7.1 to 8.9 times in a 5-day WS. In contrast, it is between 15.8 and 23.5 times for a 7-day WS, depending on demand variability, as visible in Figure 8. Demand variability consistently influences average \(\mathrm{C_{H}}\). On average, \(\mathrm{C_{H}}\) is higher by 14.9% for SD 30 compared to SD 10 for a 5-day WS and 25.7% for a 7-day WS. With increasing R + LT value, the relative difference in average \(\mathrm{C_{H}}\) related to higher demand variability reduces with minor exceptions. On a 5-day WS, the highest relative difference for average \(\mathrm{C_{H}}\) due to higher demand variability is noticed in R + LT = 2, with a value of 40.9%, and minimal in R + LT = 25, with a value of 5.9%. On a 7-day WS, the highest relative difference for average \(\mathrm{C_{H}}\) due to higher demand variability is noticed in R + LT = 1, with a value of 64.3%, and minimal in R + LT = 30, with a value of 10.3%. Significant differences exist when comparing maximal and minimal absolute \(\mathrm{C_{H}}\) within R + LT groups. On average, differences between maximal and minimal \(\mathrm{C_{H}}\) are above 80%, regardless of the WS and demand variability. For 48% of R + LT groups (57 out of 120), differences are higher than 100%. The maximum relative difference between the maximum and minimum absolute values of \(\mathrm{C_{H}}\) in a 5-day WS occurs for R + LT = 21, with values of 129.3% for SD 10 and 149.9% for SD 30. In a 7-day WS, differences are even bigger, 249.5% for SD 10 in the R + LT = 6 group, and 122% for SD 30 in the R + LT = 15 group.