In a pierce-frame build the spear shafts pass through holes in the top, bottom and any mid rails instead of being welded to the rail face. The rails are punched or drilled before assembly, and a punch schedule is the list that tells the shop where: the size of each hole (the shaft section plus a small clearance) and the position of every centre measured from a datum, usually the outer face of the first stile.
The hole clearance is a fine setting: too tight and the shafts will not seat after welding or powder coating, too loose and the weld has to bridge a gap. A schedule of ordinates is faster and less error-prone than dimensioning each hole on the drawing.
The first and last shafts must clear the stiles, so the schedule also tells you whether the end spears sit inside the frame.