South Deals E-W Vul	♠ 9 ♥ Q 3 ♦ Q 8 6 ♣ A K J 9 8 7 6
♠ J 10 7 5 ♥ J 10 8 6 4 ♦ 9 7 ♣ 10 2	N W   E S	♠ A Q 8 ♥ A K 9 2 ♦ J 5 4 2 ♣ Q 3
	♠ K 6 4 3 2 ♥ 7 5 ♦ A K 10 3 ♣ 5 4

 

 

For the above hand posted on the 5th March, the "rule of 20" was postulated as a tool for considering opening the South hand at the 1 level, eventually concluding that as the total of the sum of the two longest suits and HCP only added up to 19 the hand shouldn’t be opened at the 1 level.

A problem with this advice is that the  "rule of 20" is not mentioned in the New Zealand Bridge Manual as an acceptable method of hand evaluation for Green, Blue, or Red systems.

Instead, the NZB manual states simply in clause 24.6 (g) (ii) the following:

(g) Yellow Systems ‒ highly unusual methods (HUMs)

A system that exhibits one or more of the following features, as a matter of partnership agreement.

(ii) An opening suit bid at the 1 level that may be weaker than a pass.

Using the "rule of 20" by partnership agreement to open 1 level suit bids regularly would mean that hands with as few as 7 to 10 HCP could be opened. This could only be done as a non-yellow system provided that a pass in opening position was also 7 HCP or less. Otherwise, and more likely,  a partnership agreement to use the “rule of 20” meets the definition of a Yellow system.

Those partnerships playing non-Yellow systems that don't state that they use the "rule of 20" on their systems cards, but where one or more of the partners regularly use this rule enough to have become an undisclosed partnership agreement, need to be especially vigilant that they are not playing an undisclosed Yellow system.

Similarly, those pairs playing 11+ HCP 1 level suit bid opening on their system cards and also pass a flat 11 HCP hand but regularly open 10 HCP 1 level suit bids non-vulnerable versus vulnerable, say, enough to have an undisclosed partnership agreement need to be especially vigilant that they are not playing an undisclosed Yellow system.