Summarize this content to 2000 words in 6 paragraphs in Arabic Stay informed with free updatesSimply sign up to the Life & Arts myFT Digest — delivered directly to your inbox.The most important question to ask yourself when considering building a digital version of a 75-year-old hydraulic computer is also the most obvious: why? Thankfully, in the case of Bill Phillips’s wonderfully inventive contraption, that question is easy to answer. First, there’s the historical value of the machine itself. It is a triumph of analogue technology, constructed at a time when electronic computing was in its infancy. With only 14 machines ever built, and just three of them operational today, it’s an obvious candidate for digital preservation.Second, the Phillips machine has enduring value as a teaching aid. In 2017, Kristin Forbes, then an external member of the Bank of England’s Monetary Policy Committee, said she regularly referenced the Moniac in her classes at MIT, praising it as “an entertaining way to teach basic macroeconomic relationships”. High-school students are introduced to the concept of the “circular flow of income”, the movement of money around an economy as it facilitates the exchange of goods and services. There is still no better demonstration of that in action than the Phillips machine, its interactivity brings the concept to life more vividly than any textbook can. But not many students will ever see an original machine demonstrated, let alone be able to interact with it.Several years ago, a colleague of mine at the Financial Times, Bob Haslett, started an ambitious project to create a digital version of Phillips’s machine that would run inside a web browser. Like me, Bob had long been fascinated by the device and was keen to see a digital version. To his immense credit, he managed to produce a working prototype. But we realised that on Bob’s version, with sliders and checkboxes replicating the tactile valves and controls of Phillips’s machine, there was a significant problem.More than half of the FT’s digital audience access the website through their mobile phones, so the content has to work on 4- to 5-inch screens. Shrinking a 2-metre-tall interactive machine into such a small screen would never work for users. It’s thought by some psychologists that viewing minified content on mobile reduces readers’ attention and cognitive reflection, and can even suppress emotional engagement: the complete opposite of what most people experience when they see — and hear — a real Phillips machine in action. The project was reluctantly mothballed.That is until last year, when technology offered an escape from the tyranny of tiny screens. On June 5 2023, Apple announced a new mixed-reality headset, the Apple Vision Pro. The tech company described it as its first spatial computer, “the beginning of a new era for computing”.Reaction was mixed. Critics pointed out that mixed-reality headsets weren’t new and the device was overpriced. Enthusiasts pointed to the quality of its 23 million pixel display, spatial audio and seamless blending of real-world and virtual elements. I could only think of one thing. It’s perfect for a digital Phillips machine.Allan McRobie is a professor of structural engineering at Cambridge university. In 2003, he restored the economics faculty’s original Phillips machine and since then has regularly demonstrated it. While restoring the Moniac, McRobie found himself alternately baffled and delighted by the ingenuity of Phillips’s design. “Real Heath Robinson” is how he described one feature that allows a water-level reading to control the vertical motions of the machine’s “Propensity to Consume” graph.In early November last year, McRobie received an email from a group of Phillips machine enthusiasts at the FT (Bob and me) and WongDoody, a design agency owned by the Indian tech company Infosys. It asked two questions, one very familiar to McRobie, “Can we come and see your Phillips machine?”, the other less so, “And can we measure it?”WongDoody used millimetre-precision measurements, reference photogrammetry and LiDAR scans of McRobie’s restored machine to produce a 3D model using Autodesk Maya, a software package typically used for creating graphics for video games and CGI for TV and movies. Textures and materials used in the original machine were carefully recreated using photographic references. The model was then loaded into Unity, a cross-platform gaming engine, where the digital machine could be brought to life. Modelling the flow of pink water in its veins was made easier by a 2017 academic paper that provided a comprehensive view of the machine’s operations.A teaser app for iPad was produced and briefly demonstrated at the World Economic Forum in Davos in January. The final app, running within the mixed-reality environment of Apple Vision Pro, is a faithful reworking of a Mark II Phillips machine from 1950. A life-sized machine can be placed on to any flat surface and powered up, either in “freeplay” mode or via guided lessons which explain economic concepts.Just as Phillips might have justifiably claimed when he introduced his machine 75 years ago, the result is economics as you’ve never experienced it before. Alan Smith is the FT’s head of visual and data journalism. 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