Diagram A shows the tradional method of topping: cutting the whole node off cleanly, to induce the stalk to split into two. But diagram B indicates to make the cut below the center of the node, leaving about 10% intact. This is the key, because the vegetation left behind has cells that are rapidly dividing in many different directions. This can lead to as many as EIGHT tops from a single pruning.
Additional image contributed by: Bubbasix
Additional image contributed by: Foz