It was a cold winter afternoon early in 2004, and we were in the midst of doing some of the first usability tests with a working, clickable prototype of the Ribbon.  (Prior to that, most of our prototypes had been paper-based.)

This particular prototype was put together in PowerPoint as a fairly inexpensive way to mock up a basic Ribbon and to see whether people got the concept.  Basically, we put a picture of each tab of the Ribbon in a separate slide in the PowerPoint deck.  We turned off the "click to advance" functionality for each slide, and then drew a nearly transparent square around each tab of the Ribbon.  Each of these squares was hooked up to an action so that clicking on them advanced to the slide that revealed the picture of the tab you were clicking on.

In this way, we were able to simulate a tabbed user interface just by drawing 8 or 10 pictures.  None of the commands within the Ribbon really worked in these early prototypes; we just would watch and listen to see where they clicked within the tab.

The Ribbon is made up of tabs (click to view full picture)

Anyway, this afternoon our subject came in to the usability lab.  I don't remember his name; I'll call him "Bob."  Middle-aged and friendly, he was one of our least experienced test subjects, yet he caught on to the Ribbon paradigm quickly.  Soon, he was finding the target features faster than anyone in previous tests, zooming from tab to tab as efficiently as we could imagine.  Especially when he was asked to find features repeatedly (to test the learnability of the design), Bob was able to whisk to his target tab and acquire the requested feature extremely fast.

My colleagues and I were back in the usability control room, watching Bob's performance on TV, so we couldn't see exactly what he was doing with the mouse.  But we could tell something was up.

So, after the test, the usability engineer started the debrief with Bob, asking how he liked what he used.

"Great!" he replied.  "I especially love the way you can use the scroll wheel of the mouse to riffle through the tabs; it's so fast and easy!"

All of a sudden, we realized what had happened.  Although we turned off the "click to advance" functionality in PowerPoint, it still has a built in behavior in Slide Show mode whereby scrolling the mouse wheel one tick advances your show by one slide.  Reversing it takes you back by one slide.  Because we had each of the Ribbon tab pictures in order in the slide deck, Bob was able to use the scroll wheel to browse through and acquire any tab he wanted.  This was a totally unintentional and coincidental feature of the prototype, yet it was Bob's favorite part of the new UI.

Bob went on his way and we never saw him again.  Unbeknownst to him, he helped design a major part of the interaction design of the Ribbon.  Although we didn't get it working in time for Beta 1, in current builds you can use the scroll wheel to zoom between the tabs, just as Bob envisioned.  It's great for quickly jumping to a tab, clicking a command, and then flicking your finger all the way up to get back to the main tab.  It saves me clicks and time.  (Using the scroll wheel below the Ribbon still scrolls the document, of course.)

Although the fact that many tabbed web browsers use the scroll wheel to switch tabs means that we might have thought of it anyway, I like to think of this as the feature Bob invented.

Thanks, Bob!