Check out Don Schlesinger's illustrious 18 and fab 4 indexes in Blackjack attack. Or just google illustrious 18. Check out gamemaster online blackjack school for more indexes.
Good luck
Vytas
The index will tell you when to deviate from basic strategy. For example, when the count is +4 or above you would stand with 15 vs 10. Even though BS tells you to hit, the count tells you that there are lots of high cards left in the deck so you are better off standing.
At +4 or above you can also split tens vs 6 and double down on 10 vs 10 and A.
This question gets asked a lot. If you're dealt 16vT off the top of a freshly shuffled deck, the count is no longer zero. It's barely negative.
This decision is very close, and that makes the difference.
That's why zero index numbers can be different than basic strategy.
If you hold a 10,6 vs 10 then the count, based on those three cards, is -1. Since it is negative you would want to hit. However, if the count was +2 before that hand started then it would have dropped to +1 so you would stand.
Overall, the best play (if you don't know the composition of the deck) is to hit because most of the time the count will be negative. That is why BS tells you to hit even though the index is zero.
Right. In either case you will be standing when the count is positive because there are more high cards that will bust you. When the count is negative you will be hitting because there are more low cards that will help you.