The illustration above is a page from "A Stereotaxic Atlas of the Rat Brain" by Pellegrino, Pellegrino, and Cushman, Plenum Press 1979.
This is a coronal section taken from a rat brain oriented in the plane of de Groot. The number in the top left corner specifies the AP coordinate with respect to bregma. The scale along the left side allows you to determine the DV coordinate with respect to bregma. The scale along the bottom of the page is used to determine ML coordinate from bregma or the midline. The number in the top right hand corner and the scale on the right side of the page allow you to determine the AP and DV coordinates with respect to The IAL or intra-aural line, a rarely used reference point.