To polar align my Vixen Polarie camera mount using a polarmeter, I first needed to know the deviation between Magnetic South and True South at the observing location.
How to find that? Well, you need to know the geographic coordinates of both your observing location and the South Magnetic Pole, which enables the bearings to be calculated.
The easiest way to find your observing coordinates is by using Google Earth. The MAS observing field at Stargard has the coordinates:
34:05:00 S, 150:33:44 E
I then obtained the coordinates for the South Magnetic Pole from Wikipedia and in 2007 they were:
64.497 S, 37.684 E
To determine the direction of the South Magnetic Pole, I used a free amateur radio software programme called 'WinGrid,' which works out the bearings of one location from another:
Screen shot of Wingrid with coordinates for Stargard and the South Magnetic Pole.
This tells me that True South is 11.2 degrees east of the South Magnetic Pole (and is 2176.6 km away) at our Stargard observing site. So by setting the latitude on the polarmeter, levelling it and adjusting the compass direction to 168.8 degrees, I should get the mount aiming fairly closely towards the South Celestial Pole.
Bubble almost level. Polarie pointing to 170 degrees. Almost there!
WinGrid is downloadable here.
EDIT 23rd January 2013: Using the I-pad app, Declination, I get a significantly different answer of 12.38 degrees, so I need to do more research.
I found the 2010 coordinates for the South Magnetic Pole (64d 25' 12" S; 137d 20' 24" E) and (using Wingrid) I got a similar answer of 11.5d deviation for 2010, still nothing like the I-pad data.