Along with a level, a levelling staff is also required for levelling. The levelling staff is a rectangular rod having graduations. The staff is provided with a metal shoes at its bottom to resist wear and tear. The foot of the shoe represents zero reading. Levelling staff may be divided into two groups:
(i) Self reading staff (ii) Target staff.
(i) Self reading staff: This staff reading is directly read by the instrument man through telescope.
In a metric system staff, one metre length is divided into 200 subdivisions, each of uniform thickness of 5 mm. All divisions are marked with black in a white background. Metres and decimetres are written in red colour [Fig 15.4 (a)]. The following three types of self reading staffs are available:
(a) Solid staff: It is a single piece of 3 m.
(b) Folding staff: A staff of two pieces each of 2 m which can be folded one over the other.
(c) Telescopic staff: A staff of 3 pieces with upper one solid and lower two hollow. The upper part can slide into the central one and the central part can go into the lower part.
Each length can be pulled up and held in position by means of brass spring. The total length may be 4 m or 5 m [Fig. 15.4 (b)].
(ii) Target staff: If the sighting distance is more, instrument man finds it difficult to read self reading staff. In such case a target staff shown in [Fig. 15.4 (c)] may be used. Target staff is similar to self reading staff, but provided with a movable target. Target is a circular or oval shape, painted red and white in alternate quadrant. It is fitted with a vernier at the centre. The instrument man directs the person holding target staff to move the target, till its centre is in the horizontal line of sight. Then target man reads the target and is recorded.