What should be the 51st 'thing that made the modern economy'? - BBC News
Tim Harford chose 50 essential inventions that shaped the modern economy, but what should be the 51st?
But what did we miss? What should be the 51st thing that made the modern economy?

We've received hundreds of suggestions, which we've whittled down to a shortlist of six. You can vote for your favourite, and the winner will feature in a special programme and podcast on 28 October 2017.

The first option of our six traces its history to 1960, in Minnesota in the US.

Dorothea Parry was ironing when her husband, Forrest, came home from work at the computer giant IBM.

How was his day? Well, he had a problem. IBM had worked out how to encode information on magnetic strips. They wanted to fix the strips to plastic cards. But he couldn't work out how.

Dorothea could. She ironed them on.

Behavioural economists say we spend differently on plastic compared with cash

The addition of the magnetic stripe was a huge boost for credit cards, which were just a few years old and struggling for acceptance. Merchants shown a Diners Club or American Express card had to phone the bank. IBM's magnetic strip paved the way for a far less cumbersome approach.

The new credit cards were pushed aggressively. And people soon found that having a "flexible friend" could make us drop our financial guard: behavioural economists tell us that spending on plastic is psychologically much easier than spending cash.

The price of convenience has been ballooning household debt. But it's hard to imagine the modern economy without them.

Our second suggestion also requires heat to manufacture, but a household iron won't do the job. You need temperatures of 1,700C to make glass.

Who first did that is lost to history, but they probably lived in Egypt, Syria or Mesopotamia, about 5,500 years ago.

Did they look at sand and have an unlikely brainwave: "I wonder what would happen if we melted it?" Or did they discover glass by accident, perhaps while smelting bronze?

Who knows? But it's safe to bet that the early glassmakers could never have predicted how it would shape the economy.

And if you choose glass as the 51st thing, my challenge will be choosing how to tell its story.

Glass touchscreen technology has driven the development of smartphones and tablets

Perhaps you're reading this on a touchscreen device, accessing the internet via fibre-optic cables. Is that the story of glass?

Or I could focus, so to speak, on the lens - how the telescope and microscope changed our knowledge of the world.

Spectacles, windows, or fibreglass could each fill an episode of their own.

One of the real challenges when choosing my list of 50 was that so many inventions overlap, one bright idea later enabling another.

The story of clocks, for example, concluded by observing that GPS wouldn't work without extremely accurate timekeeping.

But many of you felt that GPS deserves a story of its own, and that's our third possibility.

If you've got a smartphone, it probably has a GPS receiver. There are 31 satellites flying around the Earth right now, constantly transmitting their position and the time.

If your phone can pick up signals from at least four of them, it can do some clever maths to work out where it is, and plot its position for you on a map.

Like many of our 50 things, GPS has military origins: the US Department of Defense developed it to win the Cold War.

Now, in turn, GPS is enabling bright ideas that will make the economy of the future - new business models that connect buyers and sellers, and new technologies such as self-driving vehicles, robots and drones.

The fourth item on our shortlist begins with an old story about a flood. It's not the Judaeo-Christian tale of Noah's Ark, but the Chinese story of Emperor Yu, the founder of China's first dynasty 4,000 years ago.

Noah floated on the waters, but Emperor Yu tamed them, recruiting an army of labourers - along with a dragon and a giant turtle - to assist in setting up irrigation and drainage.

The traditional irrigation system used in Bali's Jatiluwih rice fields has Unesco world heritage status

Great Yu changed China, and irrigation continues to shape our economy, from California, where arguments rage over the most valuable use of scarce water, to Bali, where the intricacy of the water-management system has astonished visiting experts.

The only woman to receive a Nobel Memorial Prize in economics, Lin Ostrom, spent much of her life studying irrigation systems.

Ostrom was fascinated by how humans cooperate to manage common resources. There are few more important questions than that - and few better case studies than how we decide who gets how much water, as it trickles - often crossing borders - from the hills down to the sea.

Paper was one of our 50 things. Should we add the pencil to the list? It does have a special place in the history of economic thought.

In 1958, the libertarian economist Leonard Read published an essay called I, Pencil, in which an ordinary pencil explained the miracle of its existence.

The humble pencil can demonstrate the sophistication of the modern globalised economy

The pencil boasted cedar from Oregon which had been milled in California, graphite from Sri Lanka, a brass ferule, a rubber made from Italian pumice and Indonesian rape-seed oil, and more besides.

Leonard Read's point was that in a modern economy, behind even the humblest of objects was a tale of international supply chains, complex manufacturing, capital investment and science.

No one person can make a pencil from scratch, yet the miracle of market forces makes pencils available for pennies. The pencil is a small enough player on the global scale - but a perfect way to understand the sophistication of the modern economy.

Time for one more idea, plucked from a list of hundreds. But where did we store that list? On a spreadsheet, of course.

Or perhaps I should say, 'On a digital spreadsheet' - because pencil-and-paper spreadsheets used to be ubiquitous.

The accountants of the 1970s would fill out row upon row of cost and revenue assumptions. A single change might require hours - or even days - with a calculator, a pencil and a rubber.

The first electronic spreadsheet, VisiCalc, came in 1979. It was the brainchild of Dan Bricklin - a computer-savvy student at Harvard Business School. He fantasised about creating a spreadsheet that would recalculate itself.

His software revolutionised finance. Wall Street and the City of London started trading financial products that could hardly be said to exist - let alone be comprehended - without a spreadsheet.

It reshaped accountancy, destroying the jobs of clerks who had pored over paper spreadsheets. But it created new jobs for analysts, exploring one scenario after another.

We increasingly understand the world around us through numbers, and the digital spreadsheet deserves much of the credit for that.

You can vote for one of the six things listed above on the 50 Things That Made the Modern Economy programme website, where you can also see the full terms and conditions.

Voting closes at 12:00 GMT on Friday 6 October 2017, and the winning 51st thing will be announced in a special programme and podcast on 28 October 2017.