These stereotaxic manipulator arms fit on a stereotaxic frame. We have both manual and motorized manipulator arms. The manual manipulator arm controls medio-lateral and vertical positioning via lead screws, and antero-posterior movement via dovetail slide movement. A Universal Joint allows the investigator to change the angle of the probe up to 90 degrees in either the antero-posterior or medio-lateral planes. The locking mechanism on the arm holds any angle position without slippage. And of course, it also provides an absolute lock at 90 degrees vertical. You should consider an upgrade, if you currently own a vernier model stereotaxic. Purchasing a Digital Stereotaxic arm lets you upgrade your existing stereotaxic to a digital model, which will reduce the risk of human error and increase accuracy (10-rather than 100-micron resolution). The large LED display is also useful for surgeries performed in low light, or constrained environments, where reading the vernier scale is difficult.