I have dual Decks and I am aligning the magnetometers to the Decks. The manual calls for less than 0.2 degrees variance in pitch and roll. One of the Decks is very true when comparing the front face of the unit to its chassis top surface, but the second unit is out in pitch when comparing the front face to its chassis top surface. I have not quantified the amount, but it is a significant amount of the total tolerance allowed. While I could go to the trouble of measuring the extent of variance in squareness from top to front, my question is: what surface should I be using to measure the alignment of the EFIS to the magnetometer? Can I just use the top surface of each component?