In the case of a spherical mirror, all signs are taken from the pole, which is often referred to as the origin or origin point. The New Cartesian Sign Convention is the name given to this sign convention.

From the pole of a spherical mirror towards the object along the primary axis, the sign is − (negative). In front of a spherical mirror, this means that the sign is always taken as − (negative). For example, in both types of the spherical mirrors, i.e. concave as well as convex mirror  object distance is always as negative.

Behind the spherical mirror, the sign is read as + (positive). For example, if an image is generated behind the mirror, the image's distance from the pole along the principal axis is considered as + (positive).

The height of is measured above the principal axis as + (positive) and below the principal axis as − (negative).