The smallest of details February 19th, 2013 Robert Mohns

This month, a great but virtually unknown man has passed away: John Karlin.

Karlin, who worked for Bell Labs in the decades after World War II, had a doctorate in mathematical psychology, was an electrical engineer, and a professional violinist. More to the point, he largely created Human Factors Engineering, the predecessor of what we today call "usability". By studying human behavior, systematically, he found ways to make technology better fit the humans it was meant to serve.

The rotary dial telephone is a fascinating (and photogenic) example. Early dials had the numbers inside the finger holes, so you could aim for them. Worked pretty well for numbers:

Rotary phone with numbers only
(photo credit: banlon1964)

But if you aren't looking directly at it, it gets a little harder to read: 

Rotary phone, seen off center
(photo credit: Robert Huffstutter)

And when you add letters as well as numbers, it gets very tough indeed…

Rotary phone dial with letters, off center
(photo credit: sagriffin305)

The solution is obvious, right? Put the numbers outside the finger holes, like this…

rotary phone, numbers outside dial
(photo credit: Dan Buczynski)

…or perhaps like this:

rotary phone, numbers in center of dial(photo credit: Master of Telxons)

Genius, right?

Wrong. The improved phones took longer to dial!

Karlin's team investigated. It turned out that by removing the numbers from inside the finger-holes, it took people longer to find the now-empty targets.

In this next photo, can you see what they changed?

rotary phone dial, numbers, letters and dots
(photo credit: Andrew Yang)


By putting dots inside the finger holes, users could acquire and hit the target more quickly. After adding dots, Bell Labs finally saw the expected improvement in speed. And so rotary phones continued for decades with that time-saving dot.

Karlin's work at Bell Labs went far beyond just making phones easier to use. His approach to measuring and testing the interactions between humans and our artifacts was trailblazing.

Karlin wasn't alone; early researchers included Alphonse Chapanis, whose work for the army showed that pilot error could be reduced with better control design and layout; and Paul Fitts gave us "Fitt's Law". But Karlin demonstrated in wonderfully and appropriately concrete ways how the smallest of details can have a measurably huge impact.

John Karlin's work was inspiring. May he rest in peace.