Latitude constant latitude and constant longitude, which are constructed with reference to the rotation axis of the Earth. The primary reference points are the poles where the axis of rotation of the Earth intersects the reference surface. Planes which contain the rotation axis intersect the surface at the meridians; and the angle between any one meridian plane and that through Greenwich (the Prime Meridian) defines the longitude: meridians are lines of constant longitude. The plane through the centre of the Earth and perpendicular to the rotation axis intersects the surface at a great circle called the Equator. Planes parallel to the
Dell Latitude the C6x0, D6x0, and E64x0 lines, but as of 2015 this line has been discontinued and replaced by both the 5 series and the 7 series. The 15" "Premium" line was the 8 series, until the E-series merged this line with the 6 series (Model numbers being along the lines of C8x0 or D8x0). The "budget" line was the 5 series, but as of 2015 the 5 series and 7 series Latitude laptops are the primary lines of Latitude laptops. The 3 series has replaced the 5 series as the budget line. Dell has also since dropped the E from