What does "trim" mean here? The pack has yet to produce a sub four-minute miler, although one runner did trim 18 seconds off his best time. Of course, that guy wasn’t running through a desert wearing 50 pounds of gear. Still, no one in a hurry would turn down a portable tailwind. What does "trim" mean here?Context: 20140928-Jetpack Keeps You Grounded But Faster Roger Bannister broke the four-minute mile barrier in 1954 with help from a couple of pacers, runners he closely followed til his final sprint. Sixty years later just about anyone could set a personal mile record—with help from a couple of jet engines strapped to their back. The U.S. military wanted to find a way to help soldiers hoof it through hostile territory at high speeds without getting exhausted. They turned to Arizona State University’s Human Machine Integration Laboratory. Engineers there came up with an 11-pound battery-powered backpack with two electric engines. The engines spin at about 60,000 RPM, producing about 15 pounds of instantaneous thrust. The researchers see the backpack as an alternative to outfitting soldiers with exoskeletons, which would have to be tailored to fit the individual soldier. The same jet backpack could be worn by anyone with few adjustments. The pack has yet to produce a sub four-minute miler, although one runner did trim 18 seconds off his best time. Of course, that guy wasn’t running through a desert wearing 50 pounds of gear. Still, no one in a hurry would turn down a portable tailwind. —Larry Greenemeier