Doors and Windows - Hanging Pre-Hung Interior Doors

A while back, my wife and I were touring some new homes for finishing/decorating ideas. I began to notice that it was not unusual for the door jambs to not be perfectly perpendicular to the opening. This was particularly noticeable when a floor pattern (such as tile or wood planks) is at the door opening. I have hung hundreds of pre-hung doors myself and have always just eyeballed the jamb after plumbing the hinge side and adjusting the gap between the door and jamb. Recently, I came up with an idea to help assure the the jamb is perpendicular (or square to) the opening depending on how you are looking at it. I place a straightedge (such as a 2x4 or 2x6) across the opening and then use a framing square to make a perpendicular line about 2 inches from each side of the rough opening. Then, when you are nailing in shims to stabilize the jambs, there is a reference line to which you can keep the jamb sides parallel. Works for me.