The back bust measurement is a half-measurement based on the full bust measurement. It runs along the back and half way underneath the arm pit.
Pattern (sewing) - Wikiwand
Bdft ii, drafting & pattern making, unit-i, standard measurement
Here's my block. I'm new to pattern drafting and about to do my first full bust adjustment so I'd like some advice please. Details in the comments :) : r/sewing
A Complete Course in Dressmaking/Lesson 6/Pattern making - Wikisource, the free online library
A Complete Course in Dressmaking/Lesson 6/Pattern making - Wikisource, the free online library
Types of measurement, Patternmaking and Tailoring Wiki
Sewing Measurements & Taking Measurements for Sewing
More than 80,000 Vintage Sewing Patterns on Vintage Patterns Wiki
Types of measurement, Patternmaking and Tailoring Wiki
Back Bust (measurement), Patternmaking and Tailoring Wiki
Women's Saree Blouse Drafting and Cutting Procedures - Textile Learner
The perfect dressmaking system (1914) - Wikisource, the free online library
Sewing Measurements & Taking Measurements for Sewing