Used but in very good shape - holds charge and has all accessories Forerunner 305 features the powerful new SiRF GPS navigation chip for supreme accuracy, even under tree cover and between tall buildings. A coded chest strap heart-rate monitor prevents unwanted interference from other devices. View larger. The unit's GPS receiver is designed to face towards the sky when you're running. A more watch-like design makes it far easier to use and wear. Plus, the 305 is engineered to help folks train better and smarter. Training assistant tools, various distance and time alerts, and bundled Training Center PC software combine to make the device an essential part of any athlete's training program