I see more and more recessed light fixtures in ceilings these days, and they present a layout challenge when it comes time to cut the corresponding holes in the drywall. Faced with this job, I put the plastic lid from a 3-lb. coffee can to work. This size lid fits snugly over the rim of most standard recessed housings.
To use the lid, I first push a nail through the center point of the lid. Then I snap the lid over the rim of the housing, and measure from the appropriate framing members to find my center-point coordinates. Then I put the lid on the drywall to be cut, nail at the center point, and trace around it. The layout is complete.
Daniel J. Ewing, Gibsonia, PA