The notes divide quantity into continuous and discrete. A continuous magnitude has parts with a conceivable common boundary; a discrete quantity is a count or number.
Continuous quantity: a line, a surface or bodily volume, which exhibit extension.
Discrete quantity: number, such as a count of 2, 3 or 10 individuals.
A row of three books is a discrete quantity insofar as it is counted, even if the books touch. The objects themselves should not be confused with the aspect of quantity.