Replacing faulty DCS and PLC cards such as processor cards, IO cards, communication cards, etc. can be a costly affair to the company. This applies not only to DCS/PLC cards, but any electronic item used in an industry for instrumentation and control. But what makes them so expensive? What makes them different from commercial electronic products that generally have much greater processing power than a typical DCS? Is it due to their higher precision and reliability? Or is it just a simple matter of supply and demand?