level staff

A level staff is a long graduated rod, typically 3 to 5 metres in length, held vertically on the ground to measure vertical distances during levelling surveys. The surveyor reads the height of a horizontal line of sight across the staff's face, using the markings to determine how far above or below a reference point the ground lies. It is the passive partner to the surveying level itself, which establishes the line of sight.

The staff is marked with alternating bands of colour, usually red and white or black and white, in units of 0.1 metres or decimetres. Within each decimetre, finer graduations show 0.01 metre intervals. The bands make the staff readable at distance even in poor light. Some staffs use E-shaped markings at key intervals, with the vertical stem of the E forming the fine graduation lines. The face is typically painted or printed on aluminium or fibreglass to resist weathering.

Staffs come in folding versions (split into two or three sections that telescope or hinge) for portability, and rigid single-piece versions for greater stability. Inverted staffs, read upside down, were once common but are now less frequent. Some modern staffs have digital electronic readouts or reflective targets for machine reading by automated levels or laser instruments. The traditional method requires the surveyor at the level to read the intersection of the horizontal crosshair with the staff markings and call out or record the value.

Accuracy depends on staff stability, proper vertical alignment, and the surveyor's ability to read fine markings from distance. Staffs are held plumb (truly vertical) by the rod operator, sometimes using a small spirit level mounted on the staff itself. Wind, uneven ground, and poor target contrast all degrade reading precision. For high-precision levelling over long distances, two staffs are often used at different stations to close loops and detect systematic errors.

The term 'staff' comes from Old French estaf, meaning a stick or rod. In British and Commonwealth surveying practice, the tool is called a level staff or levelling staff; American usage sometimes favours 'level rod' or 'levelling rod'. The instrument has remained fundamentally unchanged since the 19th century, although modern materials and graduations have improved durability and readability.