Why Calibrate? Compass calibration is important to safe, controlled flight. It compensates for changing background magnetic "noise", a.k.a. magnetic deviation (not to be confused with declination). Deviation that isn't corrected through compass calibration will cause inconsistencies between GPS and compass that can result in "toilet bowl effect", a swirling motion that can cause the Phantom to fly out of control. What is Magnetic Deviation? Magnetic deviation is a horizontal variation that comes from the Phantom itself and the equipment you have installed on it as well as the magnetic makeup of the area you are flying in (again not to be confused with declination). Sometimes the deviation will be insignificant, but other times it can be big enough to cause you to lose control. Warning Signs The Phantom can only detect when the compass is providing extremely poor (implausible) data. This typically occurs if you place it near a strong magnetic field or do not calibrate it properly. It will flash red and yellow lights and the P3/P4 will indicate a compass error in the app. IMPORTANT: The lack of a compass error does NOT mean your compass is definitely working and calibrated properly. MOD Value This is the total magnetic field calculated using the "sum of squares" from the X, Y and Z axes. On the P2, you need to plug in the cable and use the assistant software. For the P3, you can see it in the app. It should be between 1,300 and 1,600, ideally 1,450. Check it away from magnetic influences. If it reads very high or very low, check it again in a different location. If it is still off, it could need calibration or it could be magnetized or damaged. The P4 shows it as the difference from the ideal MOD value i.e. ABS(1450 - MOD). IMPORTANT: A good MOD value does NOT mean your compass is working and calibrated properly. For example, if you calibrate next to some rebar, your mod value may still be OK until you fly away from the rebar. What Does Calibration Actually Do? Calibration measures the magnetic fingerprint of the surrounding area. By turning the compass 360 degrees, the Phantom can see where the compass reading doesn't smoothly increase or decrease. It uses this information to build an adaption table so that when the Phantom turns during flight, the reading is smooth and linear. When Should I Calibrate? You do not need to calibrate before every flight and in some cases you definitely should not calibrate. That doesn't mean you shouldn't ever bother doing it. It only takes one time for it to go very wrong. The most important aspect of compass calibration is making sure the magnetic "neighborhood" around your Phantom is consistent between calibration and during flight. IMPORTANT: The ideal place to calibrate is an open field with nothing metallic in a 20ft radius. Keep away from drainage pipes, irrigation systems, rocks, etc. DO Calibrate Mod value out of whack or compass error reported (check area first). Circling in flight or not flying straight (also check for other possible causes). New equipment added or removed / new firmware installed. Location change (greater than ~250 miles). Significant change in terrain (e.g. to / from mountains). If you just degaussed your compass (BTW, don't degauss unless instructed). DO NOT Calibrate If near concrete, buildings, and hidden or overhead power lines / pipes / etc. If you're indoors, on a paved surface, on a stone surface, on the beach, on a boat, on a balcony, near a car, near speakers, etc. If there are metallic (ferrous) objects nearby or you're not sure Pre-Calibration Checklist Everything used in flight should be powered during calibration, e.g. GoPro, tracker, etc. Remove all metal from within 10ft radius, e.g. watch, phone, ring, belt, coins, controller. Calibrate on grass or dirt and not on concrete, asphalt. Calibrate on a level surface if possible. A cardboard box is a good idea to get it off the ground and level. How to Calibrate Power up your Phantom and accessories as normal. Wait until your Phantom is ready to fly. P1 / P2: Flip S1 five times between the top two positions. P3 / P4: Select CALIBRATE in the SENSORS section of the app. Click OK. Confirm solid yellow rear lights. Pick up the Phantom and turn it smoothly and steadily a full 360 degrees until the lights turn solid green. Point the front of the Phantom straight down and repeat until the lights turn off and resume normal flashing. Note: Don't be concerned if your gimbal reacts poorly to being face down, keep turning as normal. Optional: power off and restart Phantom. Enjoy your flight! If for any reason, you do not complete any of the above steps smoothly and evenly, restart the process.