Your Simrad is likely connected to a heading sensor, which it is either set to or defaults to. The Garmin is pointed the last direction the boat traveled (NOT where it was pointed). Just like when you back up, the plotter shows the boat "pointed" in the direction of your stern, or when swinging at anchor, pointed in the direction the boat is moving. The GPS tells you what direction the boat has been moving in, not necessarily the direction it is pointed in. I regard plotters as representing a theory of where you are. The GPS coordinates on modern systems is very accurate (unless the gov is doing something with it, typically announced in the LNMs), but the match to the plotter's cartography, as shown in the examples above, may be poor. Sometimes it is the cartography, and apparently sometimes not (I have on occasion plotted a GPS fix on a paper chart that was more accurate than the the plotter, but usually they are both identical). That, to me, is why a pair of good binoculars, good depth sounders and a radar are the most important tools; they convey the reality of where you are, not a theory. I still think, at least for us, an accurate compass and a paper chart are very important back ups and adjuncts, fading perhaps in relevance but far from gone. On long trips I still like to use a big chart as a reference and as a visual log book. If the electronics go down you can quickly DR from your last plotted point. I still often take compass bearings after setting the anchor for the same reason... you never know! Another matter of personal style and ergonomics, but we, especially she, still finds it easier to steer to a given compass course, the compass being straight ahead in line of sight, rather than off the plotter, when "Otto" is not at the wheel.
