To reduce inventory costs with DOS, you need to set a target DOS for each product or product category based on your inventory objectives and constraints. This target DOS should reflect your desired service level, demand variability, lead time, and cost trade-offs. You can use benchmarking to compare your DOS with industry standards or best practices. Additionally, customer feedback can help you determine how long they are willing to wait for your products. Furthermore, you can calculate inventory turnover to determine how often you sell and replace your inventory in a given period. Lastly, the economic order quantity will help you find the optimal order quantity that minimizes your total inventory costs. Once you have your target DOS, you can compare it with your actual DOS and adjust your inventory levels accordingly. If the actual DOS is higher than the target DOS, then you have too much inventory and need to reduce it; whereas if the actual DOS is lower than the target DOS, then you have too little inventory and need to increase it.