It’s worth checking not only the formula for net debt, but also the formula for price-to-book. As a tip, I can mention that inventory value is not included in that formula.
Duell’s business is naturally heavily dependent on its inventory, the salability of its inventory products, and the value of that inventory. If you believe the inventory is valued anywhere near correctly, Duell is cheap. A different question is how quickly this undervaluation will unwind when inventory doesn’t translate very strongly into positive numbers on the income statement’s bottom line.