How do you make a computer that people will want to wear on their face? “You have to make it light,” says Isabelle Olsson, the lead designer of Google Glass, the computer-equipped eyewear. “You can’t expect people to wear goggles all day long.” Over years of trial and error, Olsson guided Glass through hundreds of bulky prototypes to its current sleek (if not necessarily stylish) look. Here’s how Google’s computer went from goggles to Glass.

2010: The first Glass prototype “was literally a backpack,” says Thad Starner, a computing professor who developed the early technology. Testers wore an augmented-reality headset strapped to a bag that held equipment including a touch pad and a Webcam. The developers also put a screen on testers’ chests to project what they were seeing through the glasses.

2011: An average pair of sunglasses weighs about two ounces. When Olsson arrived at Google, in 2011, the latest version of Glass weighed half a pound—and had a cellphone glued to its side. “One overarching theme was ‘We have to get rid of everything that isn’t essential,’” she says. She and her team whittled down everything from the hinges to the nose pads.

2012: As Glass got lighter, Olsson turned to aesthetics. When an engineer told her that a clunky camera couldn’t get any smaller, she took the prototype to a belt sander and ground off some plastic so that the camera resembled a tiny, two-tier cake. She handed the prototype back to the engineer and told him to turn it on. The camera still worked.

2012–13: During field tests in 2012, one designer heard a “bubbling” sound when he wore the glasses outside. The sunscreen he’d rubbed behind his ears was reacting with a plastic coating on the frames. Olsson and her team changed the coating, and Glass became available to the public just a few months later.

2014: Wired summed up the response to Glass’s lensless frames: “Ugly and awkward.” In January, Olsson’s team released the first pair of prescription lenses. The reaction was muted. Gizmodo called them “reasonably attractive”; New York granted, “We’re out of cyborg territory.” Olsson’s takeaway is simple: “There is nothing easy about designing for the face.”

IN THE FUTURE: Google’s face-computers might one day be even lighter. In March, the U.S. Patent and Trademark Office published a patent application in which Google claimed “a method for manufacturing a contact lens having an integrated circuit.”