''Close your eyes and dial your home phone number,'' says Gregg Vanderheiden, holding out a cardboard mock-up of a typical cellular phone.
His interviewer obliges. But when she opens her eyes, she sees she made a mess of it, punching the phone's program keys instead of digits.
''Try again,'' Vanderheiden says, handing over another cardboard phone.
This one has a raised nib on the 5 key and ridges surrounding the digits, and her fingers trace the pattern smoothly.
''Now, every key has a tactile clue and you can dial with confidence,'' he explains.