The heading device is the next key component, a compass of one type or another. Autopilots typically use the fluxgate compass, a relatively simple and reliable device which senses the direction of the earth's magnetic field by a ring core sensor in a fluxgate coil and transforms into a digital signal. To overcome errors caused by sharp turns or rough seas as well as "dip errors, a phenomena that is more pronounced as you get closer to the earth's magnetic poles, a number of manufacturers offer a hybrid fluxgate compass or "rate compass. Essentially, a rate sensor limits the effects of pitch and roll, providing more accurate steering. Relatively new, GPS compasses are setting standards for accuracy and dependability and are being used as the boat's primary heading device. Because they have no moving parts and are virtually maintenance free, they offer superior reliability. More and more larger yachts and commercial vessels are adding these units as a backup to the ultimate heading device, the $20,000 to $50,000 gyrocompass.