magnetometer technology. Several models of dive computer incorporate a compass function, but this may not be accessible at the same time as the primary decompression information, and may be limited in their precision of display information. Direct and Indirect reading compasses There are two ways in which a compass may be marked, which influence the way you would read them. These are known as direct reading compasses and indirect reading compasses. Both provide the same information to the same level of accuracy. Both types may have graduations on the card which can be read through a side window to give the bearing directly. The direct reading compass has graduations on the housing which read anti-clockwise round the face, with zero on the far side. The effect of this configuration is that if the housing is aligned with a direction, the north point of the card or needle will point directly towards the number representing the bearing. No further effort is needed on the part of the operator, you just find the number the arrow points at and read off the bearing. The bezel has no graduations, it is just a marker to align the card. The indirect reading compass has graduations on the bezel. These graduations are clockwise round the face, and the zero mark coincides with the notch. To take a bearing the compass must first be aligned with the direction, then the bezel must be turned so that the notch aligns with the north point of the card or needle, and the bearing can then be read at the far side of the compass. Electronic compasses Flux-gate compasses are built into several models of dive computer as an extra function. They may require calibration when powered up, but calibration usually lasts as long as the processor is running. They are usually insensitive to tilt as there are no moving parts to jam. The display varies, and may not be as intuitive as for a mechanical compass needle or card arrangement. They can often be calibrated to account for local deviation and give true direction. The nearby presence of a magnetic compass can cause large error, but they are not greatly affected by other electronic compasses, as can be seen from the images. Some digital cameras for underwater use also have a built in flux-gate compass (such as the Olympus TG series) which can be used for navigation as