Not that Complicated
You can swing your compass using a GPS. It is easy, cheap, fun, reasonably accurate and takes less than an hour. You can also obtain deviation. See my post below. The one thing I did not mention in the post is that there can be no current or tide. I believe the accuracy is good enough for virtualy any sailboat application, since under sail, the sailboat can have a quite of bit of leeway. Comparing the GPS and the compass, I have seen leeways in excess of 10 degrees. By the way, the term "dip" rings a bell and I might be confusing it with declination. As someone mentioned, the only two terms important to sailors are "variation" and "deviation".
You can swing your compass using a GPS. It is easy, cheap, fun, reasonably accurate and takes less than an hour. You can also obtain deviation. See my post below. The one thing I did not mention in the post is that there can be no current or tide. I believe the accuracy is good enough for virtualy any sailboat application, since under sail, the sailboat can have a quite of bit of leeway. Comparing the GPS and the compass, I have seen leeways in excess of 10 degrees. By the way, the term "dip" rings a bell and I might be confusing it with declination. As someone mentioned, the only two terms important to sailors are "variation" and "deviation".