In a normal survey shot, all measurements are taken starting at the “from” station going toward the “To” station. In the diagram, A1 to A2 is a normal shot.
It is important to understand that a normal shot goes from a defined station to an undefined station. In the diagram, the shot A1 to A2 goes from the origin, whose location is defined, to A2 whose location, at the time, is undefined. As soon the shot is processed, the location of A2 is defined. Thus each shot defines the location of a new station and a picture of the cave is slowly built one shot at a time.