Abstract: A compact, low-cost, hand-held builder's tool for use in defining reference lines perpendicular and parallel to a specified surface. The tool comprises a housing that is generally small enough to fit conveniently in the user's hand and that includes a battery-powered laser for projecting a visible laser beam through an exit window in the housing over an extended range. An on-board alignment mechanism is provided within the housing for adjusting and setting the alignment of the laser beam in fixed disposition for establishing an accurate reference line. The housing has two generally parallel broad faces joined by a plurality of connecting faces extending substantially perpendicular to the broad faces. One of the broad faces and two of the perpendicular connecting faces taken together define three reference planes that are mutually perpendicular to one another within a margin sufficiently small that the tool has an accuracy suitable for use over an extended range of at least about 20 ft (about 6.1 m).