Distance from the main sequence (D)
Alternative name for Instability and abstractness.
Distance from the main sequence, denoted D, measures how far a package sits from Robert Martin's stable-abstractions balance, A + I = 1. A high D value means the package sits far from that line. Distance alone does not identify why: use Abstractness and Instability to distinguish the lower-left Zone of Pain from the upper-right Zone of Uselessness. Treat the result as design-pressure evidence and inspect the package's role before choosing action.