The Rule of Sevens Revisited
Jeff Ward, 1982
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From Backgammon Times, Volume 2, Number 3, Summer 1982.
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Last issue I discussed the "Rule of Sevens," a helpful guide in gammon-saving situations. The idea is that with one man left to bring home, it is undesirable to have a spacing of seven points between the outside man and a gap in the home board. Whenever possible, this spacing should be avoided by continuing the outside man forward. When this is impossible, it is often better to avoid the spacing by using an ace to slot a home board gap. For example, in Figure 1, Black has a better chance to save the gammon next turn if he plays 5/4, slotting the 4-point.
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Figure 1.
Black to play 1.
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There are some exceptions. It is clearly better to move a lone outside man 13/12 rather than to slot the 5-point because the slotting play, at most, leaves only the four highest doubles to save the gammon next turn.
All but one of the other exceptions involving an ace to play concern a gap on the 4-point. An example is given in Figure 2 where Black should move 12/11 even though he moves into a spacing of seven points.
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Figure 2.
Black to play 1.
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The single exception not involving the 4-point is illustrated in Figure 3. Here, Black should continue his outside man forward with 11/10, moving into a spacing of seven points.
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Figure 3.
Black to play 1.
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If the relevant gap is on the 2 or 1-point, the Rule of Sevens always applies with an ace to play.
The Rule of Sevens also applies with a deuce to play, as long as the 1-point is empty; but never applies if the number to be played is larger than a 2. In Figure 4, Black reduces his bad rolls next turn by playing 3/1, destroying the gap on the 1-point.
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Figure 4.
Black to play 2.
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Likewise, in Figure 5, Black is better off slotting, the slightly better of the two choices being to slot the 2-point with 4/2.
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Figure 5.
Black to play 2.
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This latter example conforms with our requirement that the 1-point be empty even though the relevant gap is the 2-point. In Figure 6, however, the 1-point is not empty, and Black is better off continuing his outside man forward with 11/9.
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Figure 6.
Black to play 2.
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There are also positions, beyond the scope of this article, in which it is correct to slot an inside point for reasons other than to avoid a spacing of seven. This is another illustration of the fact that home board gaps may make gammon-saving situations complicated.
When these positions come up in real life, the player is often in a state of mild emotional panic as he contemplates being gammoned. Faced with a critical choice as to whether to slot or not, it may be difficult to do the preceise shot counts necessary to determine the right answer. That's when the Rule of Sevens comes in handy. With the appropriate positions, it provides a quick and accurate answer and hopefully, a way out of the dilemma.
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