Abstract: A plumb bob capable of marking either soft or hard surfaces is disclosed. A chalk reservoir can be attached to the bob for marking hard surfaces. Removing the chalk reservoir enables the user to insert a metal stake or headless nail into the bob, where it is held by magnetic force. Also disclosed is a slide hammer assembly that helps drive the stake into the surface. When the stake penetrates soft surfaces, its resistance to removal is greater than the magnetic force holding it in the bob and it remains as a plumb line mark when the bob is removed.