A depth-indicating device for determining the depth of insertion of a surgical tool comprising a pair of spaced apart end caps, separated by a compressed spring, with the surgical tool passing through axial openings in both end caps, and firmly attached to one of the end caps, but free to slide through the opening in the other. A guide tube is attached to the second endcap, such that the surgical tool can be guided to its operating position on a body part. The second end cap and guide tube are attached to a location having a known position relative to the body part. A tracking marker is attached to the first end cap such that its longitudinal position can be tracked using a remote racking camera. Since the surgical tool is attached to the first end cap, the tool position is also tracked by the tracking system.