The illustration above shows a rat skull aligned in the skull flat orientation. Skull flat means that the landmarks Bregma and Lambda are oriented so that they lie in the same horizontal plane. This can be achieved as follows: with a pen or electrode clamped in the electrode carrier of the stereotaxic instrument, lower the pen down to Lambda using the DV drive screw. Take the reading on the DV Vernier scale. Move the pen anteriorly and lower the tip down to Bregma. If the head is oriented to "Skull Flat" the reading on the DV vernier scale should be the same as it was at Lambda. If it is not, raise or lower the incisor bar on the stereotaxic instrument until the DV readings are the same.