Today’s subject, my readers, is Plumb Levels. These tools are the precursors of “spirit levels” simply referred to as “levels” as we know them today. Whereas the “plumb level” employs a plumb bob to function, the “level”, replaces the plumb bob with sealed, bent, spirit filled vials drawn out of glass. The subtle development improvement, and final emergence of “spirit level” as the tool of preference occurred over a long period of time, close to a century. The details of this evolution is a well documented subject taken up by another species of specialized collector. They have spots; my fur is striped.
The PLUMB BOB and LINE on its own is a tool to verify the VERTICAL. Constructing buildings, however, frequently requires verification of the HORIZONTAL and various means have been employed to turn the plumb line into a horizontal reading device.
Early in the history of the development of the plumb bob, workers learned to construct wood or metal frames, attachments to the plumb bob and line that enhances their use to verify the Vertical and others that convert them into “leveling” instruments that verify Horizontality. The plumb bob and line are hung from a very specific point on the geometry of the frame. The plumb line and sometimes the point of the bob are made to align to another predetermined reference mark on another part of the frame. Because of the careful construction and geometry of these frames, as the tool is moved to align the plumb line with the reference mark, one side of the frame becomes “level” (horizontal).
The construction of the plumb level frame must be geometrically correct for the tool to have any efficacy. The simplest are formed from one piece of material. But, because the plumb level wants to be easy to move around and store when not in use, they are frequently constructed out of many small pieces of wood or metal that must be joined together in a strong and durable fashion. It is essential that the plumb level frame maintains a consistent shape for it to be accurate for the life of the tool. In many examples you will note their simplicity to be deceptive.