Overhead cost have increased in significance over time and, in many firms, represent a much higher percentage of product cost. Assigning overhead using only unit-based drivers can distort product cost. This can be a serious matter if the non unit-base overhead cost and a significant proportion of total overhead cost. Overhead assignments should reflect the amount of overhead demanded (consumed) by each product. ABC recognizes that not all overhead varies with the number of units produced. By using both unit and non unit based activity drivers, overhead can be more accurately traced to individual products.