Editing Card counting (section)

=== Systems ===
Basic card counting systems assign a positive, negative, or zero value to each card. When a card is dealt, the count is adjusted by that card's counting value. Low cards increase the count; they increase the percentage of high cards in the deck. High cards decrease the count for the opposite reason. For example, the Hi-Lo system subtracts one for each 10, jack, queen, king, or ace and adds one for any card between 2 and 6. 7s, 8s, and 9s count as zero and do not affect the count.<ref>Axelrad (2010), p. 256.</ref>

A card counting system aims to assign point values roughly correlating to a card's ''effect of removal'' (EOR). The EOR is the estimated effect of removing a given card from play. Counters gauge the effect of removal for all cards dealt and how that affects the current house edge. Larger ratios between point values create better correlations to actual EOR, increasing the efficiency of a system. Such systems are classified as level 1, level 2, level 3, and so on. The level corresponds to the ratio between values.

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.<ref>{{cite web |title=Blackjack Side Counts |url=https://www.qfit.com/blackjack-side-counts.htm |access-date=20 March 2009 |publisher=Qfit.com |archive-date=11 March 2009 |archive-url=https://web.archive.org/web/20090311045259/http://qfit.com/blackjack-side-counts.htm |url-status=live }}</ref>

Keeping track of more data with higher level counts can hurt speed and accuracy. Some counters earn more money playing a simple count quickly than by playing a complex count slowly.

This table illustrates some example counting systems.<ref name="qfitcc2">{{cite web |title=Card Counting Strategies |url=https://www.qfit.com/card-counting.htm |access-date=10 March 2013 |publisher=Qfit.com |archive-date=10 March 2013 |archive-url=https://web.archive.org/web/20130310034023/http://qfit.com/card-counting.htm |url-status=live }}</ref><ref>{{cite book |last1=Archer|first1=John|title=The Archer Method of Winning at 21|date=1973|publisher= Henry Regnery Company |isbn=0-87980-328-2}}</ref>
{| class="wikitable"
|-
!Card Strategy
!2
!3
!4
!5
!6
!7
!8
!9
!10, J, Q, K
!A
!Level of count
|-
| Hi-Lo
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| 0
|align=center| 0
|align=center| 0
|align=center| −1
|align=center| −1
|align=center| 1
|-
| Hi-Opt I
|align=center| 0
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| 0
|align=center| 0
|align=center| 0
|align=center| −1
|align=center| 0
|align=center| 1
|-
| Hi-Opt II
|align=center| +1
|align=center| +1
|align=center| +2
|align=center| +2
|align=center| +1
|align=center| +1
|align=center| 0
|align=center| 0
|align=center| −2
|align=center| 0
|align=center| 2
|-
| KO
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| 0
|align=center| 0
|align=center| −1
|align=center| −1
|align=center| 1
|-
| Omega II
|align=center| +1
|align=center| +1
|align=center| +2
|align=center| +2
|align=center| +2
|align=center| +1
|align=center| 0
|align=center| −1
|align=center| −2
|align=center| 0
|align=center| 2
|-
| Red 7
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| 0 or +1
|align=center| 0
|align=center| 0
|align=center| −1
|align=center| −1
|align=center| 1
|-
| Halves
|align=center| +0.5
|align=center| +1
|align=center| +1
|align=center| +1.5
|align=center| +1
|align=center| +0.5
|align=center| 0
|align=center| -0.5
|align=center| −1
|align=center| −1
|align=center| 3
|-
| Zen Count
|align=center| +1
|align=center| +1
|align=center| +2
|align=center| +2
|align=center| +2
|align=center| +1
|align=center| 0
|align=center| 0
|align=center| −2
|align=center| −1
|align=center| 2
|-
| 10 Count
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| +1
|align=center| −2
|align=center| +1
|align=center| 2
|}