A fixed-length measurement accessory includes a rigid body fixed to a base supporting a magnet for magnetically coupling the accessory to a host tool. An opposite end of the rigid body provides a visual marker for alignment with an end of a workpiece. A variable-length accessory includes telescoping rigid bodies joined by a coupler. One end of one rigid body is joined to a base supporting a magnet for magnetically coupling the accessory to the host tool. The coupler houses a friction member creating light friction resisting adjustment of a combined length of the rigid bodies. An opposite end of the other rigid body provides a visual marker for alignment with an end of the workpiece. Markings are provided on at least one of the rigid bodies for indicating a combined length of the rigid bodies at multiple relative positions.