Ensure the GPS antenna is placed and configured correctly to have an accurate signal.
Most Lowrance and Simrad MFDs have an accurate internal GPS antenna. Always ensure that WAAS (or EGNOS for Europe) is enabled prior to logging data. GPS receivers typically have an accuracy of approximately 5 meters. However, actual accuracy along travelled paths is typically better than this conservative estimate because heading can be incorporated into the position estimation. You can gauge qualitative accuracy by examining the smoothness and placement of your trip path. You can be assured you have a highly accurate signal if your trip path is smooth and precisely falls within known boundaries (e.g., a shoreline or a marina).