Yeah ericks spot on. The compass will deviate with influences from iron sources, which change the magnetic flux densities around them.
In other words putting a compass near your scope is practically worthless unless you have done magnetic compass swing (on the whole setup) and corrected the compass deviations (from the setup)..This is not possible on small cheap compasses they do not have NS and EW flux variation correctors.
You best be is to use the iceinspace procedure:
http://www.iceinspace.com.au/index.p...63,405,0,0,1,0
But be aware that magnetic compass can be out by a few degrees because of what i mentioned.