At short stacks there is almost no postflop. Every hand is jam or fold. These are the unexploitable Nash shove ranges from an unopened pot — then you can drill them on a real felt.
A Nash jam chart is the equilibrium shove range: if both players play it, neither can profit by switching to a different mix. Shallower stacks jam wider. Deeper stacks tighten toward premiums.
Pick a depth and sit the grid:
Chip-EV Nash is the cash / early-MTT default. Near a bubble or final table, ICM tax makes you shove tighter (or call tighter). PokerGym’s ICM trainer exists for that second problem — don’t use a 15bb cash jam chart on the stone bubble.
Memorizing the grid is step one. Step two is taking the decision on a clock. Open Train → Push/Fold, or the tournament trainer, and grade yourself against the same Nash the chart shows.