I went to the Army store and got a real magnetic compass. I compared the compass values to both an Android compass app and a smart phone compass app. See the pictures for the results. Here in Pittsburgh Magnetic north is about negative degrees in relation to geographic north. It appears that the Android app is definetely pointing toward geographic north by 9 degrees compared to the compass. Next I borrowed my friends IPHONE and used the IPHONE app that comes with the phone. You can see that north is way off in relation to magnetic north. I then downloaded 2 more android compass apps which showed closer results compared the magnetic compass but they are off about 4-5 degrees. Only one of these apps asked me to configure the compass doing a figure 8 pattern. I also checked each setting by itself with the other devices away from each other to make sure that there was no interference going on and the results did not change. I also made sure that I was away from anything magnetic where I placed the compasses. CONCLUSION: Get a good magnetic compass to calibrate your rotorcopter!!! IF you think about it this way, if the smart phone compass can be off as much as 15 degrees, and you add in the variance of actually pointing the booms to true magnetic north can be 10 to 15 degrees, the compass on the copter can be as much as 30 degrees or more off.