Here is a great link to a tutorial that will teach anglers how to log sonar charts on several brands of GPS fish finders. Sonar logging is a great way to help fellow anglers navigate new waters, learn lakes/rivers/ocean, and get the most updated versions of your favorite lake maps. Plus, it's easy to do. Navionics launched a tutorial on how to log sonar charts.
Follow the link: http://www.navionics.com/en/plotter-tutorial