Nick go into your settings on your chart(lake map) and activate your gps grid lines. When you look at the horizontal lines you will see numbers. When we are talking about 02 line we mean 4202 horizontal line. That’s 42 degrees 02 North is the grid line number. Your lines running up and down are you’re westerly heading. We aren’t talking about those. So say the marina is 4150 line(not sure what line actually), you would have to run North to the grid line that’s says 4202. That would be approximately 12 nautical miles and 13.75 regular land miles. So if you would set a waypoint out there to take you back there to fish, it gives you both numbers(North and West) to take you back to that spot. It’s like a big piece of graph paper. These numbers are pretty specific to the area of Geneva and Ashtabula. They may be too shallow for Walnut Creek, PA or too far out for Cleveland or Huron. I’m by no means a pro at this so if someone else has a better explanation of this, please chime in. Hope this helps.