The science (or even the art!) of instrumentation is of fundamental import­ ance to engineers, scientists and medical workers. Instruments are the eyes and ears of the technologist. (His nose is reserved for detecting the effects of excess current. ) Without sensors and their associated signal processing systems there would be no modern transport, no National Grid distributing electricity, and anyone unlucky enough to fall ill would be offered only the most primitive medical treatment. The progress that has been made in almost all areas of technology can be seen in terms of the rate at which the necessary instrumentation has been developed. For example, in recent years many improvements have been made to the performance of the internal combus­ tion engine. More and more power has been squeezed out of smaller and more economic engines. One of the reasons is that in the last few years sensors have been developed which allow investigations to be made of the way in which the flame front spreads inside a cylinder after ignition. This work has led to a redesign of the geometry of the inlet valves and the piston, and more efficient engines are the result. The process of instrumentation is often considered solely in terms of the sensors used and their associated electronics. However, there are two steps involved in making any measurement. These are, first, getting the data, which is where sensors and electronics are used, and second, analysing it.