Garmin GPSMAP 172C Owner's Manual - Page 65
WAAS Capability, Receiver Status and Accuracy
UPC - 753759043537
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WAAS Capability The GPSMAP 172/172C is capable of receiving WAAS (Wide Area Augmentation System) satellite signals. WAAS is an FAA (Federal Aviation Administration) funded project to improve the overall accuracy and integrity of the GPS signal for aviation use, but land/sea based users may also benefit from this system. At this time, the system is still in the development stage and is not fully operational. There are currently two WAAS satellites that can be received in the U.S.A., one over the Atlantic Ocean and one over the Pacific Ocean, in a geo-stationary orbit over the equator. Effective use of the WAAS satellite signal may be limited by your geographic location in relation to those satellites, now in developmental service. WAAS satellite signal reception requires an absolute clear view of the sky and works best when there are no nearby obstructions such as buildings, mountains, etc. WAAS satellites are numbered 33 or higher when viewing the sky view on your GPSMAP 172/172C. Initial reception of the WAAS signal may take up to 15-20 minutes, then 1-2 minutes afterwards. When WAAS differential correction has been received for GPS satellites (numbers 32 or below), a 'D' appears in the signal bar of the sky view and '2D or 3D Differential' appears in the receiver status. To learn more about the WAAS system, its satellite positions and current state of development, visit the FAA web site (http://gps.faa.gov). Since WAAS requires CPU resources of the GPSMAP 172/172C to search for and track the satellites, you may disable the WAAS feature to improve unit performance if WAAS reception is not available in your area. To disable/enable WAAS capability: 1. From the GPS tab, press MENU, then use the ARROW KEYPAD to highlight 'WAAS Off' or 'WAAS On' and press ENTER. Receiver Status and Accuracy Receiver status is indicated at the top field of the page, with the current Accuracy and Dilution Of Precision (DOP) to the right of the sky view. Accuracy uses DOP and other factors to calculate horizontal position accuracy in feet or meters. Reference Main Menu: GPS Tab Highlight 'WAAS Off' and press ENTER to disable the WAAS capabilities. 55