Baseline grid
The body type (at 7.5pt / 11pt) dictates the baseline grid and then everything else aligns to it.
The pullquote’s type is sized so that the x-height of each character takes up one baseline increment, as does the height of the borders above and below the quote. The images, too, follow the same baseline grid. (source)
I’ve used the font property shortcut and set Georgia at 1em (which defaults to 16px) and a line-height of 1.5, which corresponds to 24px. This becomes the baseline unit. (source)
The easiest place to begin determining a basic line height unit is with the font size of the body copy. For the example I’ve chosen 12px. To ensure readability the body text will almost certainly need some leading, that is to say spacing between the lines. A line-height of 1.5em would give 6px spacing between the lines of body copy. This will create a total line height of 18px, which becomes our basic unit. (source)