Loc   Source statements                 Object code
0000  PROGA  START  0
      EXTDEF LISTA,ENDA
      EXTREF LISTB,ENDB,LISTC,ENDC
     

.1 assembled normally, a reference in this csect
.pc relative
0020  REF1  LDA   LISTA                   03201D

.4 listb is an external reference
.a modification record is created
0023  REF2 +LDT   LISTB+4                 77100004

.6 an immediate reference, local here
0027  REF3  LDX  #ENDA-LISTA              050014


0040  LISTA EQU   *


0054  ENDA  EQU   *
.8 assembler knows all but LISTC, thus computes the 14
. then creates a modification record
0054  REF4  WORD  ENDA-LISTA+LISTC        000014

0057  REF5  WORD  ENDC-LISTC-10           FFFFF6
005A  REF6  WORD  ENDC-LISTC+LISTA-1      00003F
005D  REF7  WORD  ENDA-LISTA-(ENDB-LISTB) 000014
0060  REF8  WORD  LISTB-LISTA             FFFFC0
            END   REF1


Loc   Source statements                 Object code
0000  PROGB  START 0 
      EXTDEF LISTB,ENDB
      EXTREF LISTA,ENDA,LISTC,ENDC


.2 the same instruction as above, refers to an external symbol
.assembler uses extended instruction, a modification record
.exists to add the value of LISTA to address field
0036  REF1 +LDA   LISTA                   03100000

.5 this is a local reference here
003A  REF2  LDT   LISTB+4                 772027

.7 assembled as an external reference here
. with 2 modification records
003D  REF3 +LDX  #ENDA-LISTA              05100000


0060  LISTB EQU   *


0070  ENDB  EQU   *

.9 the same expression contains no known values 
.3 modification records are generated
0070  REF4  WORD  ENDA-LISTA+LISTC        000000
0073  REF5  WORD  ENDC-LISTC-10           FFFFF6
0076  REF6  WORD  ENDC-LISTC+LISTA-1      FFFFFF
0079  REF7  WORD  ENDA-LISTA-(ENDB-LISTB) FFFFF0
007C  REF8  WORD  LISTB-LISTA             000060
            END   


Loc   Source statements                 Object code
0000  PROGC  START 0 
      EXTDEF LISTC,ENDC
      EXTREF LISTA,ENDA,LISTB,ENDB

.3 same as in PROGB
0018  REF1 +LDA   LISTA                   03100000

001C  REF2 +LDT   LISTB+4                 77100004
0020  REF3 +LDX  #ENDA-LISTA              05100000


0030  LISTC EQU   *


0042  ENDC  EQU   *

.10 same expression, LISTC is known here, relative to the 
.beginning of the program
.there are 3 modification records required
0042  REF4  WORD  ENDA-LISTA+LISTC        000030
0045  REF5  WORD  ENDC-LISTC-10           000008
0048  REF6  WORD  ENDC-LISTC+LISTA-1      000011
004B  REF7  WORD  ENDA-LISTA-(ENDB-LISTB) 000000
004E  REF8  WORD  LISTB-LISTA             000000
            END