Image caption Eileen Lim and Nicole Lee at Changi Airport Terminal 2 in Singapore

As day turns to night in Singapore's Changi Airport, a queue of people wait patiently for a picture with an old star.

They leave their bags by a bench, turn their cameras on themselves, and pose for a photo.

Some smile; some jump like starfish; one even dances. As they upload to Instagram, the old star watches on, unmoved.

And then - a noise. The moment they've been waiting for. The travellers turn their cameras round, and the star begins one last turn.

In a blur of rotation, Kuala Lumpur becomes Colombo; Brunei turns into Tokyo; and a dozen other cities whirr into somewhere else.

Two people taking photos, Eileen Lim and Nicole Lee, aren't even flying. They have come especially to see the departures board.

"It's therapeutic to see the names turn round," says Eileen, a teacher in Singapore. "And that sound - I love it."

Every time she comes to Terminal 2, Eileen takes a photo with the board. But now, she is saying goodbye.

In less than three hours, the hoardings will come up, and the sign will come down. Changi Airport, like hundreds of others already, will whirr, spin, and flap for the final time.

Media playback is unsupported on your device Media caption Listen to the sound of Singapore's last airport departure board

As the Terminal 2 queue testifies, split-flap boards are popular. They are a romantic reminder of air travel's so-called golden age; a menu of the world; a vintage prop for the Instagram era.

Put it this way: no-one is waiting for a picture by the digital displays.

But, like most vintage tech, split-flap boards are inefficient. They are harder to update and harder to maintain. They do not speak in full sentences. They do not advertise.

When Changi announced the "retirement" of their boards, they said parts - and there are hundreds of thousands in each sign - were becoming harder to find.

And so Singapore's signs, installed in 1999, have come down - as have hundreds of others, from Budapest to Baltimore. There is no list of those that survive, but designers agree they are a vanishing sight.

Even the company that gave split-flap boards to the world no longer sells them to airports.

Image copyright Solari di Udine Image caption An early split-flap board in Windhoek, Namibia, 1965

Solari di Udine, as it is now known, was founded in 1725 - more than 250 years before Changi Airport opened - in a small town in northern Italy. It specialised in clocks for towers.

After World War Two, the company began working with designer Gino Valle. He and Remigio Solari developed a sign with four flaps, each containing ten digits - perfect for telling the time.

The now-familiar design, with white numbers on black flaps, won the prestigious Compasso D'Oro award in 1956. In the same year, Solari sold its first moving sign to Liege railway station in Belgium.

With the help of Belgian inventor John Myer, the design evolved to 40 flaps, which, like the clocks, turned via motors and currents.

Now able to display words as well as numbers, the Solari board was ready to take over the world.

Image copyright Solari di Udine Image caption Solari di Udine's signs at Liege, 1956

The company sold "thousands" of boards to airports and railway stations, says marketing manager Katia Bredeon - even in hard to reach markets.

"When there were the economic protection rules in Japan, the only product using non-Japanese technology was the Solari split-flap board," she says.

Solari was not the only manufacturer - on the other side of Europe's Iron Curtain, for example, Czech company Pragotron made similar products - but, like Hoover, the Italians became synonymous with their design.

Although the company remains an industry leader, and still sells to airports and railway stations, the signs are now electronic (thin-film-transistor and light-emitting diode).

But - despite the march of technology - Gino Valle's split-flap board has not died out. In fact, this Italian design is having a renaissance.

Image copyright Solari di Udine Image caption Jorge Newbery Airport, Buenos Aires, Argentina, 1960

While some airports still have Solari boards, they are often museum pieces, kept because of inertia or Instagram.

In Australia, for example, there are three working boards in the Qantas first class lounges in Sydney and Melbourne.

"They were nearly glassed over, but the sound is too important," the airline said in 2016. "Our guests love to hear them as well as see them."

But these days, you are more likely to find Solari boards away from airports, rather than inside.

Solari di Udine still sell their boards to "shops, restaurants, museums, and hotels". Others, too, are tapping into the sepia-tinted nostalgia scene.

Image copyright Solari di Udine Image caption Accra, Ghana, 1969

In 2013, six engineers who worked together at Drexel University, Philadelphia, formed Oat Foundry - a company that built "cool mechanical things for brands and companies".

Three years later, they were approached by a "fast-casual" restaurant who wanted to display orders in a "non-digital way...without guests bathing in that blue light glow".

The client suggested "an old-school train departure board", and, after four months of research, they had a prototype.

The product was a mixture of old - they tested a number of materials "to get that iconic sound of 1960s airports and stations" - and new: it was integrated with an iPad point of sales system.

Image copyright Solari di Udine Image caption Osaka, Japan, 1965

Soon after advertising their product online, they got their second split-flap client - the Chicago Cubs Major League Baseball team.

"And that's when we knew we were on to something," says Jeff Nowak, marketing manager.

They now have "thousands and thousands of modules" on "nearly every continent". So the question is - why do split-flap boards still appeal?

"It depends on who you ask," says Mr Nowak.

Image copyright Solari di Udine Image caption Grand Central Terminal, New York, in 1966

"The utilitarian loved that the sound signalled the changing of information. They can keep their eyes on the morning paper and only need to look up when necessary.

"For those who live in a city with an original split flap, the sound recalls a wistful memory to days gone by. The clack-clack-clack sound represents the anticipation of travel.

"[And] for the generations that do not have a history with these displays, it is the eye-catching analogue movement."

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Last year, the final Solari board on Amtrak's US rail network was taken down - in Oat Foundry's home city, Philadelphia. There was a campaign to keep it, and it was later displayed in a museum.

For Jeff, it was a reminder that people don't always want to ride on the tails of 21st Century technology.

"You would print out and frame a hand-written or a type-written letter from Tom Hanks," he says.

"Would you print out an email from him? There is value in the tangibility of experience."

Image copyright Solari di Udine Image caption The Solari board at Idlewild airport, New York, 1962. The board has been recreated in a themed hotel at what was renamed JFK airport a year later

Follow Owen on Twitter @owenamos