Look at the textbook total-cost curve and you'll see two opposing lines cross. That's the break-even. This tool computes where ordering cost equals carrying cost on your numbers, then draws the curve so you can see how steep the trade-off is — i.e., how much you lose by ordering slightly more or less than optimum.
Total annual inventory cost = (D/Q × S) + (Q/2 × H). The first term — ordering cost — decreases as Q goes up: bigger orders, fewer POs. The second term — carrying cost — increases as Q goes up: more average inventory. The sum is U-shaped (mostly); the minimum of the U is the EOQ, and it's also the break-even point where the two terms are equal.
The curve also tells you how robust your choice is. A flat bottom means small changes in Q don't change total cost much — some flexibility. A sharp bottom means even a 10% deviation costs you real money.
Look at "Cost for ±20% deviation." If it's small (say under $500/year at this SKU), the bottom of the curve is flat and you don't need to be precise — round to a case pack. If it's large (say $5,000+), order quantity precision matters for that SKU.
For those, layer them on with the other tools.