How things work

Radio you cannot hear

How Does the Internet Cross a Room?

Wifi is radio. Your data rides on a wave wobbled in a pattern both ends agreed to read, and every device sharing that channel waits its turn.

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A siphon, not a plug

Why Does a Toilet Flush by Itself?

A toilet flushes because a sudden rush of water fills the bend behind the bowl, and a full bend pulls the rest away by itself.

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Under the floor and back

Where Do Escalator Steps Go at the Top?

The steps never end. Two guide tracks at changing spacings make them form stairs in the middle and flatten at both ends, then return underneath.

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A wave made of cars

Why Is There Nothing at the Front of a Traffic Jam?

Most traffic jams have nothing at the front: one small braking spreads backwards down the line as a wave and never quite fades out.

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Carrying heat out, not cold in

How Does a Box Make Itself Cold?

There is no such substance as cold. A fridge squeezes a gas hot to dump heat out behind it, then lets it expand cold to soak up some more.

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And that is the boring half

Your Phone Beats the Computer That Flew to the Moon

The computer that landed Apollo 11 had less memory than one photo, and it was enough — because it did one job perfectly rather than everything adequately.

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Throwing air downwards

Why Does a Wing Hold a Plane Up?

A wing throws air downward and the air shoves back. Lift grows with the square of speed, so twice as fast is four times as much of it.

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A compass painted on the ground

Why Are Runways Numbered?

A runway's number is its compass heading divided by ten, so a pilot lining up can check the direction against the instruments.

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Lighter than air, and too slow

Why Did Airships Stop Flying?

Airships float because their gas is lighter than air, but they were too slow and too big for weather, and aeroplanes overtook them.

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Wide, narrow, wide

How Does a Shop Scanner Read a Barcode?

Guard bars differ at each end, so a label scanned backwards still reads. The stripes carry no price at all — that lives in the shop's own computer.

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A sealed tank of chemicals

Why Does a Battery Run Out?

A battery stores reacting chemicals rather than electricity, and that reaction can only happen a fixed number of times before it is spent.

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Constant, invisible steering

Why Does a Moving Bike Stay Up?

The forks are angled so the front wheel trails behind the steering axis and turns into a fall by itself, curving the bike back upright.

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Turning speed into heat

How Does Rubbing Stop a Car?

Brakes do not remove a car's energy, they convert it. Pads squeeze a spinning disc and all that movement leaves as heat the disc sheds into the air.

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Two shapes that do not fold

Why Do Bridges Have Arches and Triangles?

Bridges use arches, triangles and cables because those shapes turn bending, which materials are bad at, into pushing or pulling, which they handle well.

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A queue that eats itself

Why Do Buses Come in Threes?

Buses bunch because a late bus meets bigger queues and falls further behind, while the one behind it finds empty stops and catches it up.

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Counting light in tiny buckets

How Does a Photo Get Caught?

A photo is a count of light: the lens focuses it, the shutter times it, and a grid of tiny wells measures how much landed in each one.

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Raise the water, not the boat

How Does a Boat Go Uphill?

A lock does not lift a boat. It seals the boat into a chamber and changes the water level, so the boat simply keeps floating at a new height.

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A shove converted to a spin

How Does a Bang Turn a Wheel?

Burning fuel shoves a piston down a tube, and a crankshaft bends that straight shove into the round motion the wheels actually need.

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Three feet always land

Why Does a Chair Wobble When a Stool Never Does?

Any three feet reach the floor together, because three points settle a flat surface between them. A fourth has to match a surface decided without it.

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Electricity needs a full loop

Why Does a Switch Turn Things On?

Electricity only flows around an unbroken loop, so a few millimetres of air anywhere in that loop stops every last bit of it at once.

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Something that always takes the same time

How Does a Clock Know When a Second Has Passed?

Every clock is built around one thing that repeats at an unchanging rate — a swinging weight, a quartz crystal — and a counter for the repeats.

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Someone else's computer, in a shed

Where Is the Cloud?

The cloud is not in the sky. It is racks of computers in big cooled buildings, holding copies of your files and a vast electricity bill.

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A desk and a filing cabinet

Where Does a Computer Keep Things?

A computer has two places to put things, and the difference is what happens at power-off: fast memory empties, slower storage does not.

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Instructions, and nothing but

What Is a Computer Program?

A program is exact instructions run in order, with tests and repeats to change the path, followed by something that understands none of it.

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A see-saw with a concrete end

Why Doesn't a Crane Tip Over?

A tower crane is a see-saw about its mast: a block of concrete on the short arm balances whatever hangs from the long one, distance included.

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Rain, stored on a hillside

How Does a Dam Make Electricity?

A dam is a battery filled by the weather: it holds rain high up and lets it fall through a turbine, turning the height it loses into power.

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Oil that refuses to be squashed

How Does a Digger Lift So Much?

Oil cannot be squashed, so pressure from a small piston reaches a much larger one, which pushes proportionally harder. That is the whole arm.

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A circuit that completes itself

What Happens When You Press a Doorbell?

The button is not the bell. It is a gap in a circuit your finger closes, letting current turn a coil into a magnet that swings a hammer.

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Only lifting the difference

Why Does a Lift Need a Counterweight?

A counterweight balances almost all of the car, so the motor only ever lifts the difference between the two — a small fraction of the whole load.

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A relay, not a delivery

How Does an Email Find You?

An email is not carried to you. It is handed from server to server using the part after the @, and waits until your device asks for it.

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Something has to break first

Why Do Fuses Blow?

A fuse is the weakest part of a circuit on purpose: a thin wire that melts before the cable behind it can ever get hot enough to burn.

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A magnet, some wire, and movement

How Is Electricity Actually Made?

Every generator on Earth does one thing: it moves a magnet past coils of wire. Run the same machine backwards and it is a motor instead.

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Four clocks and some arithmetic

How Does a Phone Know Where It Is?

Nothing tracks your phone. It times signals from several satellites, turns each delay into a distance, and solves for the only point that fits.

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A fan and a hot wire, in that order

What Is Inside a Hairdryer?

A hairdryer is a fan and a coil of thin wire — and hair dries because moving air carries water away, not because the air is hot.

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Adding a wave to its own mirror

Why Does Noise-Cancelling Work?

A predictable engine drone can be anticipated and cancelled, but clattering cutlery is different every time and mostly gets through regardless.

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Stopping the cabin spinning

Why Does the Little Tail Rotor Matter?

Spinning the main blades twists the body the other way, so a small rotor on the tail pushes sideways to cancel the twist and hold the nose still.

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Buying time, by millimetres

How Does a Helmet Protect a Head?

A helmet does not make your head harder. It crushes, which stretches a sudden stop over more time and cuts the force a brain must survive.

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The same bag, holding less

Why Does Hot Air Lift a Balloon?

Heating the air drives some of it out of the open mouth, so what is left inside is about a fifth lighter than the air outside the balloon.

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Millions of tiny corrections

How Does a Computer Learn?

Nobody writes the rules for recognising a cat. The computer guesses, is told how wrong it was, and nudges its own numbers a million times.

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Somebody else's computer

Where Does a Website Actually Live?

A website is not in the air. It is files on a real machine somewhere, reaching you as small addressed packets handed from router to router.

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Steam that flips a switch

Why Does a Kettle Switch Itself Off?

Steam runs down a hidden tube to a strip of two bonded metals, which bends as it warms until it snaps the power off behind your back.

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Rows and columns, checked constantly

How Does a Keyboard Know Which Key You Pressed?

No wire runs from every key. They are wired as a grid and scanned hundreds of times a second, so twenty wires find one key among a hundred.

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A set of heights, not a shape

Why Does Only One Key Fit?

Every notch on a key lifts one spring-loaded pin to exactly the right height. Get all of them right at once and the barrel is finally free to turn.

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Rope gripping rope

Why Does a Knot Hold?

Nothing in a knot is glued or clipped. Pulling the rope squeezes its own crossings together, and rope pressed on rope refuses to slide.

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A wire too hot to stay dark

How Does Electricity Become Light?

Only the filament is thin, so the current squeezes there and pours out white light near 2,500°C. An LED skips the heat entirely.

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Steel on steel, barely gripping

How Can One Engine Pull a Two-Kilometre Train?

Steel wheels on steel rails barely rub, so one engine can pull an enormous train — and barely grip, so it cannot stop quickly.

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Lifting half the threads

How Does a Loom Turn Thread Into Cloth?

Weaving is not sewing: long threads are held tight, half of them lifted to open a gap, and a crossing thread is shot straight through it.

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A speaker running backwards

How Does Your Voice Get Recorded?

A membrane thinner than paper flexes when your voice hits it, and that movement is measured thousands of times a second into a list of numbers.

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Twisting water molecules

Why Does a Microwave Heat Food, Not the Plate?

A microwave flips a radio field billions of times a second and only water molecules follow, so wet food heats and a dry plate does not.

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Splitting atoms to boil a kettle

How Does Nuclear Power Work?

A nuclear station is an ordinary steam power station with a very strange fire: split atoms make the heat, control rods hold the rate steady.

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Dry heat, and a reaction

Why Does an Oven Brown Food?

Boiling water and an oven reach similar temperatures and only one makes toast, because dry heat lets the surface climb past a hundred degrees.

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Guessing is done by machine

Why Do Passwords Have to Be Long?

Nobody sits typing guesses. A computer tries billions a second and every human trick first, so length beats cleverness every single time.

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Sheets that slide off

Why Does a Pencil Leave a Mark?

The name comes from a 16th-century find people mistook for lead. More clay in the mix means fewer sheets come away, which is what makes a line fainter.

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A hole, a lens and a very short while

How Does a Camera Freeze a Moment?

A photograph is light let in for a fraction of a second and recorded before anything in front of the lens had time to move and blur it.

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Three pins, three different jobs

What Is Happening Inside a Plug?

A plug has several pins because electricity needs a way in, a way back, and an escape to the ground, plus a fuse designed to fail on purpose.

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Pushed hard so less is lost

Why Are Power Lines So High Up?

Power lines carry electricity at enormous voltage because that wastes far less on the journey, then transformers step it back down.

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Almost all of them boil water

How Does a Power Station Work?

Coal, gas and nuclear stations look nothing alike and all do one thing — boil water, so the steam spins a magnet inside coils of wire.

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Dots, fired one at a time

How Does a Printer Place Ink So Exactly?

A resistor boils a speck of ink for a few millionths of a second and the steam bubble shoves one drop out. Black is added because three inks make mud.

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A wing going round in circles

How Does a Propeller Pull a Plane?

A propeller blade is a wing bent into a circle. Instead of lifting upward it lifts forward, throwing air backward and never once stopping.

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A wobble carried on a wave

How Does Music Get Into a Radio?

A station sends out one steady wave and wobbles it in time with the sound; your radio picks that wave alone and reads the wobble back off.

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A light you cannot see

How Does a Remote Control Reach the Television?

Infrared will not pass through a sofa but bounces nicely off a pale ceiling, which is why aiming a remote at the wall so often works anyway.

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Sense, decide, move

What Makes Something a Robot?

A washing machine follows instructions; a robot senses what is actually happening and decides what to do about it, many times a second.

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Two pushes and a leftover

How Does a Boat Sail Into the Wind?

A sail turns wind into a mostly sideways push, the keel refuses to go sideways, and what is left over carries the boat forward, even upwind.

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Two levers and a travelling point

Why Do Scissors Cut When One Blade Cannot?

One blade alone cannot cut, but two levers squeezing from opposite sides can — at a single point of contact that travels from pivot to tips.

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One foot always down

Why Is a Scooter Easier Than a Bike?

A scooter is easier than a bicycle because you stand low with a foot free, so a wobble is corrected instead of becoming a fall.

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Millions of tiny lights

Why Are Pictures Made of Dots?

Nothing on a screen ever travels anywhere. Red and green side by side read as yellow, and your eye cannot separate them, so it reports the mixture.

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A ramp wrapped round a stick

Why Is a Screw So Hard to Pull Out?

A screw is a ramp rolled into a spiral, turning many easy rotations into one enormous squeeze. Pulling it straight out fights the whole spiral at once.

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Two threads that catch each other

How Does a Sewing Machine Stitch?

The needle never carries thread all the way through. It pushes a loop under the cloth, and a second hidden thread is hooked inside that loop.

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Light knocking electrons loose

How Does Sunlight Become Electricity?

Each packet of sunlight can knock one electron loose, and a solar cell is layered so that every freed electron flows the same way out.

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A magnet shoving paper

How Does a Speaker Make Sound?

A coil carrying the recorded current becomes a magnet, dragging a paper cone in and out so it shoves the air at exactly that rhythm.

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It falls there, mostly

How Does Water Climb to the Tap?

Water reaches your tap because it is stored higher than your house, and that height alone is what supplies the pressure inside the pipes.

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Sound turned into electricity and back

How Does a Voice Travel Down a Wire?

A telephone turns the air's vibration into a matching electrical wobble, sends that down a wire, and turns it back into sound.

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Mostly by not being sent

How Does a Picture Get to Your Television?

A moving picture is far too much to send, so almost all of it is thrown away: only what changed, and only what your eye would notice, makes the trip.

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A switch that feels the room

How Does a Heater Know When to Stop?

A thermostat is just a switch that temperature opens and closes, which is why a room drifts slowly above and below the number you set.

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It notices charge, not pressure

How Does Glass Feel Your Finger?

A touchscreen never notices pressure. It measures charge draining into the salty water you are made of, at every crossing of a wire grid.

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Grip, not speed

Why Do Tractors Have Huge Back Wheels?

A tractor is built to pull, not to travel: huge rear wheels give the grip that pulling needs and spread the weight so it does not sink.

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A wire loop under the tarmac

How Does the Road Know You Are Waiting?

The saw cuts in the road just before the stop line hold a loop of wire whose field changes when metal parks over it. A bicycle barely disturbs it.

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Cones, not lips

Why Do Train Wheels Never Fall Off?

The inner lip hardly ever touches the rail. Leaning outward in a bend puts the outer wheel on a wider diameter, so it covers the extra distance itself.

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Spreading the load

Why Do Trucks Have So Many Wheels?

Road damage depends on what each wheel presses down, not on the total, so a truck spreads thirty cars' worth of weight across many axles.

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Not stronger. Just patient

How Does a Tiny Tugboat Move a Huge Ship?

A tug cannot outmuscle a container ship and does not have to: floating removes the weight, so a small push held for minutes moves anything.

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Hold the roof up before you make it

How Do You Dig a Tunnel Without It Falling In?

The hard part is not removing the rock but stopping everything above from arriving in the hole, so the lining goes in as fast as the digging.

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A very small parachute pointed the wrong way

Why Do Umbrellas Turn Inside Out?

An umbrella inverts because wind flowing over the dome lifts it from outside, and the ribs only brace against downward force.

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Not through the sky

The Internet Runs Along the Sea Floor

About 99 per cent of international internet traffic crosses the ocean floor by fibre-optic cable rather than satellite — and ships have laid it since 1858.

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The room does the pushing

Why Does Suction Pick Things Up?

Nothing sucks. The fan throws air out of the exhaust, the hose drops below room pressure, and the room's own air pours in carrying the dust.

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Redrawn sixty times a second

How Does a Video Game Work?

A game is not a moving picture. It reads your controls, recalculates its whole world and draws a fresh still image sixty times a second.

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Water carrying straight on

Why Does Spinning Get Clothes Dry?

A spin cycle throws nothing out. Water keeps travelling straight while the drum forces the clothes to curve away, so it leaves through the holes.

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Pushed from below, never pulled

How Does Water Get Up to the Top Floor?

Nothing can suck water higher than about ten metres, so tall buildings push instead: a pump flings it out and a narrowing pipe presses it up.

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One push, turned sideways

Why Does a Sharp Edge Cut So Easily?

A wedge redirects your downward push sideways and concentrates it onto almost no area at all, which is the whole of why a sharp edge cuts.

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Three blades, and each one is a wing

How Does a Wind Turbine Work?

A turbine blade is not pushed by the wind, it is lifted sideways like a wing — and no turbine can take more than two-fifths of the wind's energy.

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A clock that survives being carried

Why Can a Watch Work on a Moving Arm?

A watch replaces the pendulum with a wheel swinging against a fine spring, which does not care which way up it is or how much it is jolted.

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A Y-channel and a wedge

What Actually Joins a Zip?

Nothing inside a zip's slider ever changes: a Y-channel hooks the teeth together one way and a wedge prises them apart when you pull the other.

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