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Measurements

Digital Measuring Instruments

Consider the two clocks shown in the diagram below.

A

B

To use clock A we observe the position of the "hands" as they move past the markings on a circular scale. The face of this clock is an analogue display*. Clock B tells us the time by displaying numbers (digits) which change at regular intervals. This is a digital display. Notice that the analogue display gives us the possibility of estimating the number of seconds whereas the digital display tells us only hours and minutes.

Similarly, we might use a voltmeter having a pointer which moves across a scale (an analogue meter) or one having numbers which change according to the voltage applied to its terminals (a digital meter), as shown below.

Again, the analogue display gives us the possibility of making an estimate when the pointer lies between two marks on the scale but, in this case, a suitable choice of calibration of the digital meter has given us greater precision.

* It is worth remembering that an ordinary "ticking" clock is, in a sense, a digital instrument with an analogue display. If you look closely you might see the minute hand moving in small steps.

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