"What’s the best way to use a GPS to pick a heading that keeps me on course to my destination?" - Chris S.
“If you have GPS, the two numbers you need to see are the desired track and actual track. If you’re centered on course and these match, you’ll stay perfectly centered on course.
Desired track is your course over the ground from your departure to your destination, or the course between two waypoints if you’re not going direct. This is what you flight plan and what you see in the DTK field of many panel-mount navigators or the course shown on many iPad apps. Track is your actual path across the ground at that moment, given your current heading, speed, and the actual winds. This is denoted TRK on many navigators.
Now imagine the course you want to fly from Airport A to Airport B is 270. This means your desired track is 270. You take off and turn on course with a heading of 270 so that you’re centered on the magenta line for the moment. If there was no wind, your track would also be 270, but today there’s a wind from the North and your track is 260. Even though you’re currently on course, you will drift south of course.
Fix the issue by turning 10 degrees right. Check your track. If it’s 270, this new heading will keep you on course. If 10 degrees was too much, your track might read 272. Turn back to the left two degrees. Keep doing this until track and desired track match. Continue making corrections as you fly and you’ll stay perfectly on course to your destination.
Note that some apps will show a suggested heading that takes into account forecast winds. You want to match the actual course, not the suggested heading.”