of units, accreditation systems and documentary standards systems. We describe what
they do and why they are there.
1.2 Measurement
1.2.1 What is a measurement?
Measurement is one of the most fundamental tasks carried out by humans, or any other
species. All knowledge of the world is gained through the senses, and our ability to
survive comes from our reactions to that knowledge. Our curiosity, intelligence and
self-awareness are adaptations that allow us to prepare for the unexperienced, and our
sensors and measuring instruments extend our knowledge of the universe beyond that
acquirable from our senses alone.
For those of us working inside corporate organisations survival and risk have slightly
different meanings from the biological sense, but whether we or our organisations make
measurements for commerce, control or curiosity the ultimate motivation is the same:
improving survival and minimising risk.
One way of identifying the reason for making a measurement is to determine how
it affects our actions. For commercial measurements, the answer is simple because
measurements are the basis of contracts. A buyer agrees to pay for a certain quantity
of goods and his or her decision on whether to buy or not depends on the quantity and
price. In commerce, measurements affect decisions about sale and purchase.
Measurements are often associated with control or regulatory mechanisms. In airconditioning
systems, temperature measurements determine whether heat flows are
increased or decreased. Measurements of rust in cars control their roadworthiness,
and measurements of toxicity control the quality of the environment. In each case
the measurements precede decisions to increase or decrease, reject or accept, or to
prosecute or not prosecute.
With curiosity-driven measurements the decisions are less obvious. In science,
experiments are used as the basis for developing and testing theory or models of
phenomena, and at each stage of the development a scientist makes a decision: does
this work, does that work, what if we do this, etc.? Eighty years after Einstein published
his general theory of relativity researchers are still making measurements to test the
validity of the theory. Again measurements are made to aid in the making of decisions.
The accepted metrological definition of a measurement is in two parts:
Measurement:
The set of operations having the object of determining a value of a quantity.
Result of a measurement:
The value attributed to a measurand obtained by measurement.
While these two definitions are technically correct, they are so because of a tautology.
The dictionary definition of a quantity is something that has a value, and a measurand
is the thing being measured. Consequently, these are self-evident statements rather
than definitions. More importantly, they are not especially helpful in distinguishing