Blackjack is a game that is most often played with six-to-eight decks shuffled together and mixed in a shoe. Whether that shoe is favorable to the player or to the house largely revolves around one factor—how many ten-value cards remain in play. The original question was, exactly, as this: 'Dealing yourself a blackjack (Ace AND Face-card or Ten) from a single deck'. The calculations above are accurate for this unique situation: ONE player dealing cards to himself/herself. The odds of getting a natural blackjack are, undoubtedly, 1 in 21 hands (a hand consisting of exactly 2 cards).
Once coming to the card counting skill with hi-lo system, we need the parameter of the number of remaining deck to get the true count. There are some estimation by number of players, rounds dealt, and other factors, rather than by sight though I’ve never heard of that any player try to keep counting the actual number of dealt cards. Actually, the trouble is not worth the reward, since it needs more complicated mathematical calculation during the blackjack game. In stead, you can train your eye to estimate the remaining decks with good accuracy in a short time rather than keeping counting. I assume that deck estimation is an important course for the players to be familiar with so as to calculate the true count for blackjack playing and betting. A great master of the deck estimation skill would increase the return of profits from casino.
Deck-estimation is definitely something that from my point of view should be practiced regularly with real cards (If possible, playing cardsfrom casinos and discard trays would be the best option), as we practice other blackjack skills. In terms of the theoretical advantage, which kind of total recall would yield over perfect deck estimation, either full, half, or quarter deck? Computer sims that calculate the true count using the exact number of cards and one that uses 1/2 deck estimation doesn't show enough difference to talk about after several million hands. That is, there is only minimal importance is produced between higher deck resolutions and simply calculating the true count, and the advantage you gain from perfect deck estimation is not as big a factor as the harm caused by sloppy estimation. There is nothing too desirable on the advantage.
Then anyone has the ideas on how to judge how many decks the cards on the table are, 3.25 or 3.5? It seems that there is nothing special except continuous practices. One thing you can do is go out and buy maybe ten decks of those cheap dollar store cards. They are a bit off from regular casino cards but they should be ok for this purpose. Take four decks and pile them up; then three decks and pile them up; then two decks and pile them up and one deck and pile it up. Line those piles up next to one another in that order and set them some where that you spend a lot of time. Maybe do this with another ten decks and set them in another location. So through out the day you to see these decks as you do for one thing and you become very familiar with that sight. When you come back to check those piles in other time, you remain yourselves that this is one deck; this is two decks; this is three decks; this is four decks. After a while you will finally know what is what when you see it again. The other way suggested here is to practice card cutting like some players. For one, to cut a deck of cards out of a pack of cards say eight decks here. Of course that would much better if you could accurately distinguish the half deck or even quarter-deck of cards. Honesty to say, after only a day or two of staring at these I bet you can pretty accurately estimate them to at least a half deck.
However, as for calculating the true count, it is really difficult to use the half-deck or quarter-deck resolution for conversion. It is recommended to apply full-deck resolution instead of half-deck that make the whole calculation process much easier, although practice of 1/2 deck resolution is still required. That is because resolving by half-decks would be more accurately to round to the nearest deck for the true count calculation.
Deck Estimator Blackjack Classic