Reorder point calculator with safety stock

Caveat: slow-moving and intermittent spare parts

This formula assumes demand is roughly normal and flows steadily. For slow-moving or intermittent spare parts, demand is lumpy: long stretches of zero, then a sudden order. That demand is not normal, so this normal-based reorder point tends to understate the buffer you actually need to hit the service level. Methods built for intermittent demand, such as Croston's method or a probabilistic (distribution-based) model, fit these parts far better.