When it doesn't fit, split it

Say your program has two parts, and the second part needs what the first one worked out.

Normally you'd write one deck with both parts in memory at once.

cell  contents  notes
 10      030    INP 30  cells 10-18: both parts in one deck: all of it in memory at once
 11      130    CLA 30
 12      230    ADD 30
 13      631    STO 31
 14      131    CLA 31
 15      231    ADD 31
 16      632    STO 32
 17      532    OUT 32
 18      900    HRS 00
 30      000
 31      000
 32      000

Step through the natural way in Cardigan

When that doesn't fit, split it into two tapes. The first ends with HRS 02, the operator loads tape 2 and starts at 00, and the loader lays tape 2's code over tape 1's. Here's the nice part: every cell tape 2 doesn't load keeps its value, so tape 1's answer is still sitting there waiting. Only the bigger tape has to fit, and the room the code no longer needs goes to your data.

cell  contents  notes
 10      030    INP 30  tape 1, cells 10-14: the first part: y = 2x, left in cell 31
 11      130    CLA 30
 12      230    ADD 30
 13      631    STO 31
 14      902    HRS 02  halt on 02: load tape 2
 30      000
 31      000

cell  contents  notes
 10      131    CLA 31  tape 2, cells 10-14: its own code over tape 1's; y is still in cell 31, on no card of this tape
 11      231    ADD 31
 12      632    STO 32
 13      532    OUT 32
 14      900    HRS 00
 32      000

Step through the CARDIAC way in Cardigan

Both print 84 for 21. In one deck the program needs 12 cells at once; split, the bigger tape needs 7.

A whole program split this way, step by step: programming with overlays.

From the tips in cardiac-code on GitHub. All the tips.