Compass direction is determined by the earth’s magnetic field and is offset from the true direction by a parameter called magnetic declination. The Solmetric SunEye 100/110 uses the convention that the top of the Skyline photo is south in the Northern Hemisphere (or north in the Southern Hemisphere). (Note that the top in SunEye 210 skylines may vary, due to the autocorrection feature.) In the Northern Hemisphere, the sun paths are symmetrical around the true south. So sun paths on the SunEye Skyline appear rotated relative to symmetrical. But in which direction? Also, the SunEye allows the user to enter the panel azimuth in magnetic or true, but the SunEye always displays true azimuth. Is the magnetic declination added or subtracted to compute the true azimuth?   Magnetic declination is defined in degrees offset either EAST or WEST, from North. Magnetic declination of EAST is like a clockwise rotation from north. For example, assume you are in the Northern Hemisphere and your magnetic declination is about 12 degrees EAST. If you are facing MAGNETIC South when you capture the skyline, then you are actually facing 12 degrees WEST (in the clockwise direction) of TRUE South.  Therefore, in a picture of this orientation, the sun paths would need to be rotated to the EAST (counter-clockwise) to compensate, which is what is done in the SunEye.  Also note, when the panel azimuth is entered in degrees, with the Magnetic selection, the true azimuth is calculated by adjusting the reading up or down to compensate for the declination. If the magnetic declination is 12 degrees EAST as in the example above, the true azimuth is computed by ADDING the magnetic declination (rotating in the clockwise direction) by 12 degrees, eg. from a magnetic azimuth of 160 degrees to a true azimuth of 172 degrees.  If on the other hand, the magnetic declination is 12 degrees WEST, then when looking NORTH, the magnetic field pulls the compass needle WEST, or counter-clockwise. When looking SOUTH, the compass is pulled toward the EAST, so that to correct it, the sun paths are rotated toward the EAST (clockwise). If the panel azimuth is entered with the Magnetic selection, then the true azimuth is computed by SUBTRACTING the magnetic declination (rotating compass reading in the counter clockwise direction), eg. from a magnetic azimuth of 160 degrees to a true azimuth of 148 degrees.

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