Audioscript

You will now hear part of a lecture. It is divided into sections to make it easier for you to follow.

Now, as you will remember from my last lecture, measurement is a very important element in all engineering studies. We have already talked about some of the reasons for that, and later in this lecture I intend to go into more detail about the types of calculation involved in measuring pressure. However, to begin, I want to give you a little information about some of the ways in which we can group or, more correctly, classify measuring devices. Now, what exactly are these devices?

A measuring device is a mechanism designed to find the dimensions, capacity, or amount of something. Measuring devices can be divided into groups in several ways. For example, they can be divided according to the nature of the things they are designed to measure; or they can be divided according to the type of measuring unit each device uses, or in any number of other ways.

If they are grouped according to the nature of things they are designed to measure, we might have some devices for measuring ground-up solids (such as flour, gravel, chemicals in powdered form etc.) and some for measuring things requiring linear measurement (such as measurement for dimensions). Many other possible types of things and their devices could be included: the three are mentioned only as a sample.

If we group measuring devices according to the type of measuring unit each uses, we might have the following types: linear units (feet, centimeters, inches, miles, metres etc.), volumetric units (litres, ounces etc.), weight units (grams, ounces, pounds etc.), and the units used for more specialized things such as electric current and temperature (amps, degrees centigrade etc.).

Some examples of devices that use different types of measuring units are rules, callipers and measuring tapes — all of which measure linear dimensions; balances — the most common being spring and beam balances - for measuring weight; and containers such as graduated glass cylinders found in chemistry laboratories, and the measuring cups and measuring spoons found in kitchens — all used for measuring volume.

A common example of a measuring instrument (device) used to measure more specialised things is the thermometer, which measures temperature. Typical household thermometers are those containing either alcohol or mercury. These instruments measure temperature quite differently from the way a rule measures linear dimensions, for example. The rule measures directly; the thermometer actually measures the expansion or contraction of the liquid inside it, and this is shown on a scale that is marked in units representing temperatures.