This forum has so much useful information if you search. Recently, my Airguide compass blew a bladder again (sigh!) and after some research here I saved money by not going with the problematic Precision vertical card compass and went with the SIRS unit. My thanks to Alex Clark, Cubus Maximus, augerin and Ursa Major who took the time to post photos of the SIRS installation on their airplanes. I must say this SIRS unit is" the bomb". It works so good and is so accurate I barely had to adjust it when I swung it after mounting it mid windshield as many suggested. I could not be more pleased with the outcome.