Abstract: An integral apparatus having laser sighting means embodied in a pocket sized device, for use in determining end points along ceilings and wall perimeter edges to more accurately size drywall pieces to be installed in generally non-rectangular perimeter sections of ceilings and walls. The sighting apparatus, comprises a housing having a longitudinally elongated base member and a longitudinally elongated column member, said base member and column member being at right angles to one another and joined longitudinally to one another, said base member and column member having opposing parallel and substantially flat longitudinal faces and an edge surface extending between the longitudinal faces, thereby defining at least one rail having two longitudinal perpendicular surfaces; a laser module and batteries. In a preferred embodiment, laser modules are provided at each axial end of the housing to enable beams to be selectively projected in either longitudinal direction.