Blackjack is not one game. The rules printed on the felt move the house edge and, more awkwardly for anyone learning, they move the correct play. A chart is an answer to a specific question, and the question includes the rules.
The single most important line on the felt. When the dealer hits soft 17 they draw to hands they would otherwise have stood on, which converts some of their 17s into 18s, 19s and 20s. It costs the player roughly 0.20 to 0.22% — more than every other common rule variation you will meet — and it changes about six cells of basic strategy, mostly against a dealer ace. It also shifts several index plays.
A 6:5 table pays $6 on a $5 blackjack instead of $7.50. It is the most expensive rule on a modern floor and it is not close. Nothing on this site is computed for it, and the honest advice about a 6:5 table is to walk past it.
DAS makes splitting more attractive, because each new hand can be doubled if it lands well. Without it, several pair cells revert to hitting: 2,2 and 3,3 against 2 and 3, 4,4 against 5 and 6, and 6,6 against 2. The chart here assumes DAS is allowed.
Late surrender gives back half your bet on your first two cards, after the dealer has checked for blackjack. It only affects a few of the worst hands, but those hands are common. Without surrender, every Rh cell on the chart becomes a hit.
Fewer decks favour the player slightly, but for anyone counting, the number that matters more is penetration — how deep into the shoe the dealer goes before shuffling. A count is only worth something once enough cards have been seen for it to mean anything, so a shoe cut at half is far less useful than one cut at three quarters. This trainer deals 6 decks cut 75% in by default, which is an ordinary, realistic shoe — and both are settings, so you can practise counting through eight decks cut at half if that is the game in front of you.
The rules are fixed because a chart for one game is wrong for another: index numbers in particular move when the dealer hits soft 17, so that rule, double after split and late surrender are not switches. The size of the shoe is a different matter — this chart is sourced for four through eight decks, so you can set the deck count and the cut anywhere in that range and every hand is still graded correctly.
In practice that means the trainer lets you set the things the chart does not depend on — how many decks are in the shoe, anywhere from four to eight, and how deep the cut card sits — and refuses the things it does. The engine is rules-aware, and it knows what H17 does to the chart, but a ruleset is only offered once its numbers are fully sourced. Where they are not, it says so rather than filling the gap with a plausible guess: how that is enforced.
Play this game Every hand dealt under exactly the rules above, and graded against the chart computed for them.
It is the most significant common rule variation. A dealer who hits soft 17 costs the player roughly 0.20 to 0.22%, and it changes about six cells of basic strategy as well as several card-counting index plays.
Bad enough to avoid. A 6:5 table pays 6 dollars on a 5 dollar blackjack instead of 7.50, and it is the most expensive single rule you will find on a modern casino floor.
Penetration is how far into the shoe the dealer deals before shuffling. A count only becomes reliable once a meaningful number of cards have been seen, so deep penetration is worth more to a counter than a small change in the number of decks.