Jan Adkins on relative measurement:
Plain measurement of length is necessary, established, and limited. We can agree that it is not, however, the fine delineation of intricate joinery, dovetailing, or shipboard cabinetry (where the curving hull has nearly no right angles). In this work, one part is measured against another, not written as a dimension.
Digging a bit further into shipbuilding, I discovered The Joggle Stick:
Once you try the joggle stick, you’ll never use anything else for fitting complex shapes and curves.
I argue deeply for the importance of relative measurement in CSS, and it’s nice to know that expert craftspeople have similar methods for getting jobs done.