The Pen Point Marker Source contains Co-57 in a ceramic matrix at the end of a 9.26″ (23.5 mm) anodized aluminum rod. The pen-shaped rod screws into a brass cap which shields the active point. The Pen Point Marker Source is used in tracing the outlines of anatomical features on a patient. The trace appears almost instantly on the camera display. Contained activity is supplied as a nominal value ±15%.