COMIX (COnfiguration of MIXing machines) is a system that assists members of the sales department of EKATO in designing a mixing machine which fulfills the requirements of a customer. It is used to help the engineer design the requested machine and prepare an offer that’s to be submitted to the customer. COMIX integrates more traditional software techniques with explicit knowledge representation and constraint propagation. During the process of routine design, some design decisions have to be made with uncertainty. By including knowledge from process technology and company experience in the mechanical design, a sufficiently high degree of flexibility is achieved that the system can even assist in difficult design situations. The success of the system can be measured by the increase in quantity and quality of the submitted offers.