Inventory calculator
Plan stock from your own demand.
Estimate a starting order quantity from forecast repairs, a shop-defined buffer, stock on hand, and open orders.
Use by SKU, not across a whole model family. Run the calculator separately for the exact screen route you actually stock. Your own history should drive the inputs.
Not a demand forecast: this arithmetic does not account for seasonality, lead time, cash constraints, supplier availability, returns, or changing repair mix.