Capoferro defines measure as the distance between the point of the sword and the adversaries body. He has several named measures, which I will try to enumerate.
Strettissma Misura: The narrowest measure is actually begun from a wide measure, wherein the opponent attacks and you retreat by stepping back with the left foot followed by the right. The distance Capoferro is measuring is from your sword to the opponent’s newly outstretched arm.
I feel that this is the most important measure that Capoferro discusses. Everything else he discusses is purely descriptive, useful only for explaining the actions in the plays. But this one is more about theory of measure itself. It is the realization of the idea that measure really is about the distance from sword to closest part of the body. Too often we only see measure as the distance between our forward foot and theirs.
Misura Stretta in Pie Fermo: The narrow measure of the fixed foot, that is to say when you can hit the opponent just by inclining the body and legs.
Misura Stretta: The next narrow measure is that in which you can attack with an increase of the foot.
Misura Larga: The wide measure is that in which you can attack with an increase of the foot.
Confused? Well, I am. I checked two translations and they both say the same. Seems like a waste to use two terms to describe the same thing, but as of yet I see no reason to believe that they describe different things aside my own desire for them to do so.
Capoferro then goes on to say that wide measure can be divided into one that takes a tempo and a half, one that takes a tempo, and on that only takes half a tempo.
Later on Capoferro will say,
The measure is wide or narrow; wide, when the adversary can be struck only through the extraordinary pace; the narrow is when I can strike the adversary in just pace with fixed foot.