Garmin Forerunner GPS
The Garmin Forerunner GPS runs on a SiRFstarIII high sensitivity GPS microcontroller chip which interpret signals from GPS satellites and determine the position of the Garmin Forerunner GPS. What makes the SiRFstarIII chip superior to other GPS chipsets is its Time to First Fix (TTFF) in urban or densely covered forest environments. The Garmin Forerunner 205, Garmin Forerunner 305, and Garmin Forerunner 405 all contain the SiRFstarIII chip. Read our Garmin Forerunner review to compare all three models.
How Does the Garmin Forerunner GPS Work?
The Garmin Forerunner GPS receiver extrapolates its position on Earth by timing the pings sent by the hundreds of GPS satellites orbiting in the sky above. The Garmin Forerunner GPS receiver measures the transit time of each message and uses these transit times along with the speed of light to compute the distance to each satellite. The final calculated position of the Garmin Forerunner watch is displayed as longitude, latitude, altitude, and location on a map. Although four satellites are normally required for the Garmin Forerunner GPS to find its location, if four satellites are not visible the Garmin Forerunner may re-use the last known latitude/longitude/altitude to give less accurate extrapolated answers.