Published in 1931, Your Days Are Numbered set out a full Pythagorean numerology system, deriving a person's core numbers from the letters of their name and their birth date and interpreting those numbers as indicators of personality, life path and timing, in the same broad tradition L. Dow Balliett had established a generation earlier on the American East Coast. Campbell's book is distinguished less by any wholly new technique than by its completeness and clarity as a single, self contained manual, described by later numerologists as the first textbook rather than pamphlet length treatment the modern American form of the practice had received.
The book's durability, continuously available across nearly a century, made it one of the primary channels through which basic Pythagorean numerology technique reached later twentieth century readers independent of the direct Balliett-to-Jordan teaching lineage. As with numerology generally, the system carries no standing as an empirically verified account of personality or fate; the atlas records Your Days Are Numbered as the influential and long lived popular text it is.
Unlike the Balliett-to-Jordan lineage, which developed and taught its techniques through a named succession of direct students meeting in Atlantic City, Campbell's book presents its system as a self-contained whole with no indication of a teacher or a school behind it, reinforcing the impression that she worked largely independently of the era's other organized numerology circles even as she drew on the same broad Pythagorean letter-to-number correspondences they all shared.