The butcher and the physicist

Measurement may be either an individual activity, or a social activity. I can pace out my living room as 31 q 1 in units of my own feet; Noah can be told to make an ark of length 300 cubits: if told these facts you might be able to determine these distances roughly in terms of feet or metres. But their utility to others as measurements relies on standardisation.

Science-based engineering relies on measurement, so people at differing times and places can agree on the properties of substances and artefacts, and develop procedures to make use of them. The essence of a measurement is that it provides absolute information that is not subject to the whim of opinion. To achieve this, it is necessary for people to agree on universal standards.

Much of modern measurement relies on electronic instrumentation. It is this area that Klaas Klaassen's book addresses. He takes a modern systems view of the technology and the abstract theory behind electronic methods of measurement.

Mathematical error theory is covered; the philosophy of measurement is discussed; electronic transducers, displays, and all the paraphernalia of modern instrumentation are laid out in front of us. A distinction is made between the resolution of an instrument and its accuracy; good to see this in a modern book dealing with digital displays of eight and more digits. To someone used to making measurements over many years, there is much that is familiar, eclectically chosen from the vast range of examples available to the 1980s author and drawn from modern electronic instrumentation.

Many people arrive at their measurement activity with only the haziest of notions of how the figure on the scale or in the display relates to what it is they are really trying to measure. If the instrument looks modern and flashy, there is a tendency to judge its accuracy by its appearance. This book gives the student a glimpse behind the front panel and the display.

But I am reminded of the story about a butcher who hires a physics undergraduate for the summer vacation. The butcher returns to find the undergraduate equipped with a planimeter for measuring the area of a piece of steak; with a depth gauge for measuring its thickness; and a balance and a pan of water for determining its density. Apparently the student is attempting to cut off a piece weighing 16 ounces for a customer. Perhaps he learned his measurement techniques from a systems-orientated textbook. The butcher eyes the meat, takes a deft cut with a sharp knife, and hands over 16 1/8 ounces.

Anyone hoping to learn the practical skills behind measurement technique from this book will probably be disappointed. But it contains a useful overview of the considerations behind many instruments we use daily and probably take for granted. A thorough understanding of the principles behind an electronic instrument, the trade-offs made in its design, and the limitations of the conversion from physical measurement to displayed quantity is an insurance against making serious errors.

An important part of the trade of an engineer is to be able to put confidence limits on his/her judgement. This book will help in that process. How many politicians and managers can have the same quantitatively derived confidence in their own judgements?

David Jefferies is senior lecturer in electronic and electrical engineering, University of Surrey.