This invention is an improvement over the prior art in that precise locating of ceiling points (corresponding to predetermined floor points) can be achieved. The structure of claim 4 in which said pointer is removably, magnetically coupled to said tube to constitute said calibration means. The structure of claim 5 in which said weight is magnetically coupled to said tube.ħ.

The structure of claim 4 in which said calibration means includes a weight adapted to be attached eccentrically of said tube axis.Ħ. An optical plumb bob comprising a base equipped with pivot means, an optical tube pivotally mounted on said means for movement in a plurality of horizontal directions, said tube including a light source, a cross hair scope and lenses so as to deliver a light ray upwardly and project a cross-hair on a ceiling, the bottom of said tube being equipped with calibration means for directing a pointer associated therewith to a floor point vertically aligned with said ceiling point.ĥ. The method of claim 1 in which said calibration includes applying a magnetic weight eccentrically to the axis of said optical plumb bob.Ĥ. The method of claim 1 in which said calibration includes repositioning a magnetically coupled pointer.ģ. In a method for determining spot locations on ceilings vertically above spot location on floors for the installation of hangars and the like, the steps of locating a floor point and a ceiling point in vertical alignment, positioning a ray delivering optical plumb bob having an adjustable pointer at the lower end thereof so as to center the ray on the ceiling point, calibrating the plumb bob so as to direct a pointer at its other end toward the floor point and, with the plumb bob so calibrated, locating thereby at least one other point on said ceiling vertically above a predetermined point on said floor.Ģ.

Dewalt plumb bob laser