Four corners drill

This text is quoted from Guy's book The Medieval Longsword. p184 https://guywindsor.net/book/the-medieval-longsword/

The first multiplier is called the “four corners drill”, and is hinted at in the set-up for the base four. First, with the defender remaining in tutta porta di ferro, the attacker changes the guard of origin and therefore usually the line of his attack, from his right shoulder, to his left, then his left hip, then his right hip. Note that these last two are the set-up for the break and the exchange respectively. The attacker may choose any guards he knows that start from these points (both donna and fenestra are coded for by “shoulder” for instance), and may cut or thrust as he likes. Then the defender starts from each “corner” in turn while the attack remains constant (mandritto fendente from posta di donna). If you expand this to include the centreline guards (mezana porta di ferro, breve, longa), you get a total of 144 combinations! This is bound to throw up problem areas, such as “how do I defend from donna sinestra against a mandritto fendente?”. You might have noticed that you can look on Second Drill as a variation of First Drill, using the four corners multiplier. It starts with the same attack, but a different starting guard for the defender.