One can also use Polaris (the North Star) at least in most of the northern hemisphere where it is visible. A long time ago, I went outside after dark and looked at how my house lined up with Polaris. In my case, it was a dead sight along the front or back side and the peak of the roof to Polaris. If it's not, you could use a protractor to determine the difference. I have done that, relative to the E/W lines of the side of the house, to point the TV antenna to 125 degrees toward the transmitter site for this area.
Jerry N0JY
Joseph, Check out this page: http://www.thecompassstore.com/decvar.html# There's a link on that page to plug in your Zip code and figure declination, or you can use the handy map on the main page. For Austin, the magic number is 4 degrees.
If I recall correctly (it's been a few years), I set the rotor control box to North, went up on the roof and rotated the *mast* until the ants pointed to magnetic north (using a compass). Note that the compass will read inaccurately if held near a metal mast. Then I rotated the mast a bit more so the ants were pointing about 4 degrees *West of magnetic North*.
That's the way I remember doing it.
Bill N5AB