IBM 1620 Manual page 85

Machine will loop in the failing subroutines using the
factor or factors being used when the fai lure occurred.
A
shorter loop using only the subroutine that failed can
then be developed by stepping through the last instruc-
tion of the subroutine before the fail ing subroutine and
then dumping FAC. Using this as one factor, write a
progrnm as follows: '
Insert - 36 0031 00100 - Release, Start - Type
in dumped FAC - Insert 00000 26 00060 00040,
00012 (Instruction located at IR-2 address),
00024 49 00000.
The machine may be single cycled through the subroutine
instructions. The customer Fortran listing containing
machine language instructions for these subroutines at
the end of the listings may be used to check machine
operation, instruction, by instruction{ or the subroutine
may be looped at high speed for scoping. The "P"
address of the branch and transmit immediate instruction
at the IR-2 minus 12 address is the address of the first
instruction of the subroutine. If this address is below
08300, it is not relocatable. Check the address in
Figure 5 to find wh ich subroutine is being used. If
this address is above 08300, it is relocatable. To tell
which relocatable subroutine is being used, check the
address with those in Figure 6.
7.9