are the costs of activities undertaken to support individual products or service regardless of the number of units or batches in which the units are produced. In the Plastim example, design costs are product-sustaining costs. Over time, design costs depend largely on the time designers spend on designing and modifying the product, the mold, and the process. These design costs are a function of the complexity of the mold, measured by the number of parts in the mold multiplied by the area (in square feet) over which the molten plastic must flow (12 parts × 2.5 square feet, or 30 parts-square feet for the S3 lens; and 14 parts × 5 square feet, or 70 parts-square feet for the C5 lens). As a result, the total design costs allocated to S3 and C5 depend on the complexity of the mold, regardless of the number of the number of the units or batches of production. Plastim can't avoid design costs by producing fewer units or running fewer batches. Plastim's ABC system uses parts-square feet, a product-sustaining cost-allocation base, to allocate design costs to products. Other examples of product-sustaining costs are product research and development costs, costs of making engineering changes, and marketing costs to launch new products.