For a long time I thought our house pretty much faced north (well within a few degrees). I need to know the angles to get an idea of what to do for the solar design of the house extensions.
But where we live True North and Magnetic North are not the same. According to the Australian Government web site they are about 11 degrees different.
Australian Geomagnetic Reference Field Computation
Requested: Latitude -37o 49′ 4.3″, Longitude 145o 21′ 54″, Elevation 870 km, Date 2013/04/18
Calculated: Latitude -37.8179o, Longitude +145.3650o, Elevation 870.00 km, Epoch 2013.2932 (Actual – 37.817884S, 145.365076E)
Magnetic Field Components
D = 10.931 deg
dD = -0.003 deg/yr
My question the was, foes the iPhone compass measure true north or magnetic north? Well it turns out the iPhone compass does both. You just tell it which one to say. I made sure it was set to true north and whalla! The angle of the house was measured. I was surprised to find it faces so much to the east.
The house actually points about 27 degrees east of north.