Indie Developer · Glasgow, Scotland
James Thomson
He has been shipping the same calculator since 1992. The app is older than Mac OS X, the iPhone, and the App Store it now lives on.
He has been shipping the same calculator since 1992. The app is older than Mac OS X, the iPhone, and the App Store it now lives on.
In late 2025, James Thomson was doing what he has done for most of three decades: working on a new version of PCalc, then quietly pushing out a 4.11.1 maintenance update. No funding round. No pivot. No fifteen-person team. Just a developer in Glasgow, his wife as the other half of the company, and an app that refuses to be finished.
PCalc is a scientific calculator. That sentence undersells it the way "a guitar with six strings" undersells a luthier's life work. It has Reverse Polish Notation for the engineers, a tip jar for the rest of us, a constants library, conversions, and a fanbase that will argue about button colors with the intensity of people who care. It is the calculator other developers keep on their own home screens.
Thomson runs all of it through TLA Systems, a studio whose name stands for Three Letter Acronym. He answers his own support email. He picks the icons. When a new Apple platform appears, PCalc is usually there on day one, because the person who makes it has been there since before the platform existed.
That instinct to be early is not a marketing trick - it is muscle memory. When Apple shipped Mac Catalyst, the technology for turning iPad apps into Mac apps, Thomson took PCalc through it and wrote publicly about every sharp edge he hit, the kind of field notes only someone who has carried one codebase across many years of operating systems can produce. He has watched the Mac change shape underneath him more times than most developers have shipped products, and PCalc kept running through all of it.
I confidently predict humans will never ever need a faster computer.James Thomson, on his Mac Pro - a prediction with a shelf life
The 1982 movie Tron sent a Scottish kid to buy a Commodore 64. That is the whole spark. From the C64 and a BBC Model B, Thomson taught himself to make machines do things, and by 1990 he was at the University of Glasgow studying Computing Science and learning to program the Mac.
PCalc arrived in 1992 - not as a product, but as a test. He wanted to understand how to build software for the original Macintosh, so he built a calculator. It was supposed to be disposable. He handed it out free, a calling card in the hope that a big company might notice. One eventually did.
After graduating in 1994, he spent two years as a systems programmer inside the University of Glasgow's own Computing Science department before the calling card paid off. Apple brought him in during the late nineties, and he landed on work that millions of people would touch without ever knowing his name: the Mac OS X Finder and the Dock. If you have ever dragged an icon down to a bouncing row of apps at the bottom of a Mac screen, you have used something he had a hand in. In 2000 he walked away from that to bet on himself, and the bet has held for a quarter of a century.
A film about a man trapped inside a computer convinced a kid to buy one. Forty-odd years later he is still inside, and seems happy about it.
University, first job, and the studio that put him on the App Store front page - all in the same city he grew up in.
The scientific calculator that built a career. RPN, conversions, constants, themes, and a tip calculator people genuinely love.
An application dock that organized a generation of Mac desktops. Macworld Eddy finalist, 4.5 Mice, Five Mice in MacUser UK.
A dice roller born from a Dungeons & Dragons habit. Naturally, the calculator guy made the prettiest dice.
Longevity, in apps (years in active development)
At WWDC 2019, Apple walked on stage and demoed a tip calculator for the Apple Watch. The room applauded. Thomson, watching, had already shipped that exact feature in PCalc on the watch years earlier.
"Sherlocking" is the developer's word for it: the moment Apple ships your idea as a built-in feature. Most people would treat it as a gut-punch. Thomson named the feeling plainly and kept building. PCalc is still the one people pay for.
It wasn't the greatest feeling, since I've had exactly that in PCalc on the watch for years.On Apple's Apple Watch tip calculator, WWDC 2019
Selling a paid calculator in a store full of free ones is a quietly heroic act. Thomson has been candid about the unglamorous parts of indie life - the staggering piracy numbers a popular paid app attracts, and the deeper problem of discovery, where good work drowns simply because nobody can find it in an ocean of listings. He has talked through these realities in interviews rather than pretending the App Store is a meritocracy.
His answer to all of it has been the same for thirty years: make the thing extremely well, then keep making it better. PCalc earns its keep on detail - the way a button feels, the themes, the Reverse Polish Notation mode that engineers swear by, the conversions and constants that turn a calculator into a tool. It is not the loudest app. It is the one that is still here.
When people ask his opinion on Apple's own built-in calculator apps, he answers as the person with the longest possible memory of the problem - someone who has thought about what a calculator should do for longer than some of his users have been alive.
His own profile lists his interests in that order, and the last word is not a typo. Under the handle stresspanda he photographs squirrels. He plays Dungeons & Dragons, which is how a dice app happened. And he is a constant voice in the Apple community - a conference speaker and a podcast pundit on Relay FM and The Incomparable.
The voice that comes through, in interviews and online, is dry and self-deprecating. He is the developer who confidently predicted nobody would ever need a faster computer, then watched the industry make a liar of him several times over, and tells the story against himself. That tone has made him a fixture: when a new Apple announcement lands, people want to hear what the person who has shipped through every era of the Mac makes of it. He has become a kind of institutional memory for an entire platform, delivered with a Glaswegian shrug.
Stay small. Keep the calculator alive on every platform Apple invents. Answer your own email.The TLA Systems business plan, more or less