Card counting is a blackjack strategy used to determine
whether the player or the dealer has an advantage on the next
hand. Card counters are advantage players who try to overcome
the casino house edge by keeping a running count of high and low
valued cards dealt. They generally bet more when they have an
advantage and less when the dealer has an advantage. They also
change playing decisions based on the composition of the deck. (
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The Hi-Lo system is a level-1 count; the running count never
increases or decreases by more than one. A multilevel count,
such as Zen Count, Wong Halves, or Hi-Opt II, further
distinguishes card values to increase accuracy. An advanced
count includes values such as +2 and −2, or +0.5 and -0.5.
Advanced players might also keep a side count of specific cards
like aces. This is done where betting accuracy differs from
playing accuracy.
Many side count techniques exist, including special-purpose
counts used for games with nonstandard profitable-play options
such as an over/under side bet. ()