The angular difference between the geographic and magnetic meridians at any place as read on the magnetic compass; variation errors vary in time and place, but they are systematic and can readily be canceled out merely by referring to government-published variation charts; the importance of this error may be judged by this example: the variation in northern California is 20° east while in northern New York it is 10° west, thus a pilot attempting to fly between the two places who failed to correct would be off by 30°. Also known as declination error.