Computer screen image of a microcircuit, produced by a computer aided design (CAD) package. CAD is invaluable in electronics design, as it allows rapid changes to be made to the design, and instant calculations on the effect on the circuit. The circuit seen here is a micro-electronic pressure sensor. Its main use is in the exhaust manifold of a car engine. Several such sensors are linked to a small computer in the car, which then alters the operation of the engine to ensure the best fuel efficiency.