Examples of the notation used in references:
T-26.IV.4:7 (T for ACIM Text; 26 for Chapter; IV for Section; 4 for Paragraph; 7 for Sentence)
W-pI.169.5:2 (W for Workbook; pI for Part I; 169 for Lesson; 5 for Paragraph; 2 for Sentence)
C-6.4:6 (C for Clarification of Terms; 6 for Term; 4 for Paragraph; 6 for Sentence)