A square or rectangular chassis, typically 1 m by 1 m internally, that is used on archaeological sites to assist with accurately planning features, objects, or structures. The chassis comprises rigid wooden, metal, or plastic sides that are drilled at regular intervals to allow a grid of criss‐cross strings to be formed in the centre of the frame. Grids are typically 10 × 10 cm or 20 × 20 cm. Sophisticated planning frames may be equipped with extendable legs at each corner and a spirit level on two of the sides in order to level the frame and thus reduce parallax. By laying the frame over an area that is to be planned or drawn, and locating the corners by off‐sets or triangulation, the planner can carefully observe the material to be drawn in relation to the grid within the planning frame and transfer this to scaled squares on the drawing board.