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That new app of ours, Bistromath, sports a custom numeric keypad for entering prices. This isn’t unusual; you’ll have seen something similar on almost every Finance app in the App Store because the iPhone’s standard 12-button numpad lacks a decimal point. What’s unusual about ours (beside Bil’s dogged persistence to make it the best custom keyboard iPhone OS 3.1 can handle, bar none) is the order of the keys: most iPhone apps arrange their buttons like a calculator with the top row ordered 7-8-9, while Bistromath’s are laid out like a telephone with the 1-2-3 on top.

This decision wasn’t arrived at lightly, mostly because I couldn’t make a choice until I knew why there were two options in the first place! It seemed mysterious and arbitrary and, frankly, stupid that they could be so similar and still so different. Were calculators optimized for math, and phones optimized for mental recall? Or were they both just mechanical artifacts of a bygone era, like the analog clock face or the QWERTY keyboard? I did some research, and found the answers in an old American Scientist article by Henry Petroski that I’ll summarize here (It’s behind a paywall, my apologies).

Calculators

Calculators inherited much of their design from the mechanical adding machines of yore, which had their keys arranged in long columns like a steampunk abacus. Each column was a power of ten (meaning an eight column adder could handle numbers just shy of one hundred million) with the numbers nine through one spilling down the column in descending order. The higher numbers were literally higher on the machine.

When the big adding machines gave way to ten key adders, and then to electronic calculators, the columns were collapsed into a single numpad. The high-to-low descending order stayed as it had on the columnar design, and it’s understandable why. After all, if you were trying to transition an existing customer base from one adder to another, wouldn’t you try to keep it friction-free as possible?

Phones

If you’re Ma Bell, the answer to that question is “no.” Bell Labs started playing with the idea of a push-button telephone in the 1950s. They knew the rotary dial wouldn’t last forever, but weren’t rushed to replace it because speed to market is not a pressing concern for monopolies. They wanted to do it right.

Bell’s scientists produced a massive variety of dialers and tested them all on ordinary people in a lab setting. They were trying to find the best possible numpad by measuring input speed, error rate, and people’s stated preference. They tried circular layouts, triangular layouts, buttons arranged in rows, in columns, and grids. The now-familiar 7-8-9 and 1-2-3 layouts were both tested as part of this Numpad Battle Royale.

The fastest dialing speeds were found with layouts that aped the existing rotary dial, and the most user-preferred layout was long, with two horizontal rows. But the eventual balance of speed, error rate, user preference, and practicality put the 1-2-3 grid on Bell’s phones, and the world followed.

So?

To this day we’re stuck with two numpad layouts that are incredibly similar, but just different enough to slow you down when you switch between them. Apple’s phone uses the 1-2-3 layout, and their Calculator app uses 7-8-9 (though its appearance has more to do with Dieter Rams than anything else).

Most of our competitors arrange their buttons like a calculator, and probably with good reason. Lots of professional types—payroll clerks, accountants, cashiers—use a 7-8-9 layout for hours a day, and Bistromath’s layout probably frustrates them.

But most people aren’t payroll clerks or accountants or cashiers. I use a calculator maybe once or twice a week, and my Apple keyboard doesn’t even have a numpad, but there are some things we all use every day: telephones, TV remotes, ATMs, and supermarket debit terminals. These everyday machines follow the 1-2-3 layout pioneered by Bell, and we use them so often I’m willing to bet you could type your ATM PIN blindfolded. By comparison, the calculator layout is almost niche.

And that, friends, is why Bistromath has a numpad like a telephone.