Doubling down

Can someone please explain this strategy as I am having some hard time understanding it.

For an example 6D game, dealer stands on A-6

A-2 vs 4, double at a true count of 7 or higher...why is that? What are the type of cards a player hoping to hit? Since the player has A-2, my understanding is that hitting a 9, 8, 7 or at least a 6 would be nice, right? My question is what is the correlation of a true count 7. Thanks.

At a true count of 7 the dealer is going to bust on his 4 more often

Exactly. As a very rough estimate, if there are a lot of 10's left, then there's a higher chance the dealer will get a 14, and subsequently get a 24.

If the dealer's other card is either an 8, 9, or 10, then hitting another 10 will bust him.

With a lot of the soft double downs, you aren't betting that you'll get close to 21, you are betting that the dealer will bust.

If you want, I'm sure there are plenty of people here who could give you the exact mathematical advantage of doubling versus hitting on a soft hand vs. 4 given a TC of +7, and CVdata actually does give you those values when you use it to generate index plays.

The soft double is based on the fact that the dealer will bust more than 40% of the time, and you won't need a card. Then, when the dealer doesn't bust, you will occasionally win by hitting your card.

Keep in mind with A2 that two of the cards you want to hit, the 7 and 8, are uncounted. So a low TC doesn't hurt you too much.

With A/2 vs. 4, the double down index is at +3 TC for a single level count.