First of all, I want to apologize to any serious typographers for using the names of css-attributes instead of proper names. With "font-size" I mean here the defined font-size as one would in css (12px, 2em, 1rem, etc.) and by line-height I refer to the line-height defined in css (1.4, 1.2em, etc.). Here is a good overview of what line-height precisely is in CSS-terminilogy: https://iamvdo.me/en/blog/css-font-metrics-line-height-and-vertical-align
I am reading Robert Bringhurst's "Elementy of typographic style", and I am not understanding what precisely the typographical scale he is writing about should be based on.
In the internet, I find most scales are taking a specific font-size as a base, but I am questioning this approach now because of the issue of vertical-rhythm. My thinking is that if we take scales as a means of putting different sizes of type into proportion, what do we still consider as part of the type?
So my question is: do you take line-height or font-size as a base for a typographic scale, and why?