Read more Advanced PRS In addition to the Essential targets there are: Two mouse and rabbit targets to support a second round of primary antibody reagents. Comparing the 50% 2D target of the gradient array with the second level 50% targets and applying the difference to the created 3D array allows the antigen density scales to be created. The antigen retrieval measure, ARM, targets are 2D and 3D deposits of a 50:50 mix of mouse and rabbit. These show the action of the antigen retrieval as it assaults the targets seeking to remove the formaldehyde fixation. The values of the two targets are used to generate the ARM value used in QC of the antigen retrieval process.