IELTS Academic Reading Practice Test 203

Few objects of the twentieth century changed so quickly from luxury to commonplace as the digital watch. In 1970 a watch without hands, springs or gears was a laboratory curiosity; by 1980 it could be bought for the price of a meal. The transformation was brought about by three technologies developed for other purposes — the quartz crystal, the integrated circuit and the light-emitting diode — and it was carried out by electronics firms rather than by the traditional watchmakers of Switzerland. Within a decade the mechanical watch had retreated to the top of the market, where it survives today as a luxury object.

The story begins with a discovery made in 1880 by the brothers Pierre and Jacques Curie. They found that certain crystals produced a small electric charge when they were squeezed, and that the reverse was also true: a crystal placed in an electric field would change its shape. A slice of quartz cut in a particular orientation vibrates at an extremely stable frequency when driven by an alternating current. In the late 1920s this property was used to build the first quartz clocks, which were far more accurate than any mechanical timekeeper, but they filled a room and were found only in laboratories and observatories.

Miniaturising this technology took decades. The first quartz wristwatch, the Seiko Astron, went on sale in Japan in December 1969, and it still had a conventional face with hands. Its appearance alarmed Swiss manufacturers, who had dominated the world market but had invested little in electronics. Worse was to come. In 1970 the Hamilton Watch Company, based in Lancaster, Pennsylvania, demonstrated a watch with no moving parts at all: a dark screen that lit up with red digits when a button was pressed.

The Pulsar, as it was called, reached shops in 1972. Its display used light-emitting diodes, or LEDs: small semiconductor devices that glow when a current passes through them. Because LEDs consume a great deal of power, the display could not be left on. The wearer pressed a button on the side of the case and the time appeared for about a second. The watch contained no dial and no mainspring; instead a quartz crystal oscillated 32,768 times a second, and a tiny integrated circuit counted the pulses and converted them into digits.

The price was astonishing. The first Pulsar sold for around 2,100 dollars, more than a small car, and it was marketed as jewellery for the wealthy rather than as a timekeeping tool. Advertisements showed it on the wrists of film stars. Hamilton had built the watch with an electronics firm called Electro/Data, and the two companies struggled to produce the devices in large numbers, since the display modules were difficult to manufacture and many failed.

A cheaper design soon appeared. In 1973 the Japanese company Seiko introduced a digital watch that used a liquid crystal display. In an LCD, the digits are formed by a thin layer of liquid crystals whose orientation changes when a small voltage is applied, blocking or allowing the passage of light. Because the display does not generate light of its own but reflects it, an LCD uses very little current, and the numbers can remain visible all the time. The trade-off is that the display is hard to read in the dark, which is why a small lamp was later added to many models.

The consequences for the industry were severe. Employment in Swiss watchmaking fell sharply between 1975 and 1983 as inexpensive digital and quartz watches from Japan and the United States took over the lower end of the market, and the Swiss share of world production fell steeply. Many small workshops closed and thousands of jobs disappeared. Swiss firms responded by consolidating and by launching the Swatch, a cheap quartz watch with a plastic case, in 1983.

Digital watches also acquired functions that had nothing to do with telling the time. Calculator watches, with a keypad of tiny buttons, appeared in the late 1970s; the Hewlett-Packard HP-01 of 1977 was a famous and expensive example. Then came alarms, stopwatches, countdown timers and calendars that knew the length of every month. By the early 1980s a digital watch could be bought for a few dollars, and it became a common gift for children. Some models even held lists of telephone numbers, a function that vanished once mobile phones could do the same. The technology had turned a precision instrument into an inexpensive everyday object.

In the 1990s and 2000s the digital watch began to be absorbed into other devices. Mobile phones showed the time, and many people stopped wearing a watch altogether. The industry responded by adding sensors: a digital watch could measure heart rate, count steps and, with a receiver for satellite navigation signals, calculate how fast its wearer was running. Battery life, once measured in months, stretched to years. The smartwatch, which appeared in the 2010s, is essentially a small computer worn on the wrist.

What survived from the 1970s was the idea that made these products possible: that timekeeping is a matter of counting oscillations, and that a crystal, a battery and a chip can do the job more cheaply than a hundred machined parts. The hands on a dial have become a matter of choice rather than necessity.

Water is a poor medium for most kinds of signal. Radio waves, which carry Wi-Fi and mobile phone calls through the air, are absorbed by seawater within a few metres, because salt water conducts electricity and the energy of the wave is converted into tiny currents. Light penetrates further, but in the sea it is scattered by particles and absorbed, so that even in the clearest water a diver can see only a few dozen metres. Very low frequency radio can reach a submerged submarine, but only at extremely low data rates.

Sound, by contrast, travels well in water. Its speed there is roughly 1,500 metres per second, about four times its speed in air. The exact figure depends on temperature, salinity and pressure, and these variations have an important consequence: because sound travels at different speeds in layers of water that differ in temperature and depth, rays of sound bend as they pass through the ocean, in much the same way that light bends when it enters a glass of water. In the 1940s researchers discovered that at a depth of about a kilometre the temperature and pressure effects cancel out, creating a layer in which sound is trapped and can travel for thousands of kilometres.

This is why nearly all underwater communication uses sound. The device that produces the sound is a transducer: a stack of ceramic discs, commonly made of a material such as lead zirconate titanate, that changes thickness when a voltage is applied and so pushes the water in front of it. The same ceramic can act in reverse, generating a voltage when sound waves press on it, which is how a hydrophone — the underwater equivalent of a microphone — listens. Modems usually work at frequencies of a few kilohertz to a few tens of kilohertz. The choice is a compromise: low frequencies travel much further but can carry far less information, while high frequencies allow faster transmission over short distances.

Sending digital data through this channel requires a modem, a device that converts the noughts and ones of a computer message into patterns of sound. The simplest method is to represent a one by one tone and a zero by another, but more efficient schemes alter the phase as well as the frequency of the wave, so that each tone carries several bits. A typical acoustic modem today can send a few kilobits per second over a distance of a kilometre or two. Engineers sometimes describe this as a narrow pipe through which only a trickle of data can pass. That is far slower than a domestic broadband connection, and it is the central constraint on everything the technology can do.

Within these limits, acoustic links have become essential to ocean science and industry. Oil and gas companies use them to control equipment on the seabed; oceanographic observatories send measurements from instruments anchored on the sea floor to a buoy at the surface, from which the data are passed to shore by satellite; and autonomous underwater vehicles, which survey the seabed or inspect pipelines, receive instructions and report their findings while submerged. Acoustic tags attached to fish and whales transmit identifying codes, allowing researchers to follow individual animals for years. Navies were among the first to need such links, and military systems remain among the most advanced.

The channel itself is unforgiving. Because sound leaves a transmitter in all directions, it arrives at a receiver by several routes at once — directly, after bouncing off the surface, and after reflecting from the seabed — and the copies interfere with one another, a problem known as multipath. The ocean is also noisy. Ships, wind, rain and the crackle of snapping shrimp all add to the background, and in some shallow tropical waters the shrimp alone can drown out almost everything else. A moving vehicle shifts the frequency of the signal, an underwater version of the change in pitch heard when an ambulance passes. And because sound travels comparatively slowly, a message sent to a vehicle several kilometres away may take seconds to arrive and seconds more to be answered.

Power is a further difficulty. A modem on the seabed cannot easily be recharged, so it must be designed to transmit briefly and sleep for long periods, and the batteries that last longest are also the heaviest. Equipment left in the sea for months is colonised by barnacles and weed, which can muffle a transducer, and salt water corrodes almost everything it touches. A device that fails can rarely be repaired by hand: recovering it requires a ship, a winch and a calm day, so reliability matters more than speed.

Researchers are pursuing several routes around these problems. One is to move data optically: blue and green light are absorbed least by water, and a laser or light-emitting diode can carry far more information than sound, though only over tens of metres in clear water and hardly at all in murk. Another is to accept that no single link will be reliable and to build networks in which several modems relay a message between them, choosing new routes when one fails — the underwater equivalent of the internet. Others are applying machine learning to the channel, teaching receivers to recognise the distortions that a particular stretch of water imposes and to correct for them. None of these approaches can yet replace acoustic links over long distances.

A decade ago, a parent who wanted to know where a child was had few options: a telephone call, a text message, or trust. Today a phone or a watch on a child's wrist can report the child's position to within a few metres, send an alert when the child leaves a designated area, and keep a record of every journey for weeks. The software is cheap, often free, and extremely popular. Schools, too, have begun to recommend such apps to parents, and devices are marketed as a child's first phone. The question is whether it makes children safer, or merely makes parents feel safer, and at what cost to the relationship between them.

The case for the technology is not trivial. Parents worry about traffic, about children who fail to arrive at school, and about the small number of children who are abducted by strangers. A location app answers the immediate question — where is my child? — in seconds, and it can summon help. Some families use it to grant freedoms they would otherwise refuse: a ten-year-old may walk to a friend's house alone because a parent can watch the route on a screen. Used in that way, the technology can enlarge a child's world rather than restrict it.

The case against is also substantial. A device that reports a child's position every few minutes is, in effect, a surveillance system, and children generally know when they are wearing one. Being watched is not the same as being cared for, and a child who knows that every detour is visible may learn to ask permission rather than to judge risk for themselves. Trust, once replaced by monitoring, is difficult to restore. There is also a practical objection: the technology addresses the dangers that frighten parents most, such as abduction by a stranger, rather than the dangers that actually injure children, among which road traffic is far more significant. A map on a screen cannot teach a child to cross a road.

Privacy is a further concern. Details of where a child goes, when and with whom are sensitive, and they are collected by companies whose business model may depend on advertising. In many countries the law now recognises this: Europe's General Data Protection Regulation gives children specific protections, and the United Kingdom's Age Appropriate Design Code, which came into force in 2021, requires online services likely to be used by children to treat their data with particular care by default. Rules of this kind matter because location data is difficult to anonymise: a pattern of movements over a few days usually identifies a person, whatever name is attached to the account.

The technology is also less reliable than it appears. Satellite positioning works poorly indoors and between tall buildings, and a signal may place a child in the wrong street. Apps sometimes fail to update, batteries run out, and a watch left at a friend's house produces a reassuring dot in the wrong place. The result can be a false sense of security. Parents who trust the screen may therefore stop doing the things that actually keep children safe: agreeing a plan, meeting them, and knowing who they are with.

None of this means that tracking is always wrong. There is a difference between a parent who secretly installs software on a teenager's phone and a family that agrees to share locations for the walk home from school. Where the child is very young, or has a disability that makes wandering likely, the balance may plainly favour monitoring. The important conditions are that the arrangement is discussed rather than imposed, that it is temporary where possible, and that it is accompanied by an explanation of what the data are for and who can see them.

The commercial context should also make parents cautious. Companies market tracking devices directly to anxious parents, and anxiety is good for sales. Advertisements that show a child's face beside a map imply that danger is everywhere and that a purchase will remove it. The implication is false. The overwhelming majority of journeys taken by children end safely, with or without an app, and most of the harm that does occur comes from people children know rather than from strangers. Fear, after all, is easier to sell than reassurance.

My own view is that these apps are neither the menace nor the safeguard they are claimed to be. They are tools, and like most tools their value depends on how deliberately they are used. A family that agrees in advance when a child will be tracked, and that switches the software off when it is not needed, is likely to gain the reassurance it wanted without teaching the child that being watched is normal. A family that installs the software in secret, and checks it obsessively, has bought a little information at the price of a great deal of trust.

The wider question is what kind of childhood we want. A generation that grows up assuming that its movements are always visible to someone may be safer in the narrowest sense and less capable in every other. The purpose of bringing up a child is not to keep an exact record of where they are, but to make the record unnecessary. The technology will improve; the judgement about when to use it will not become easier.