Source: For Delhi Bridge Association Newsletter by Mr. S.N.Mathur
When do you pass and when do you bid over partner’s double of weak two opening is a dilemma often faced when holding a hand of medium strength, with possibility of game or handsome penalty. A simple rule of nine enunciated by Mel Colchamiro, a professional bridge player and a teacher resolves the issue to a great measure.
The rule suggests that: when you are thinking about passing partner’s takeout double, turning it into a penalty double, add together the number of cards you have in the opponents’ trump suit, the number of honor cards you hold in that suit, and the level of the auction. If the total is nine or more, pass; otherwise, bid something.
Colchamiro playing with his wife Janet in the teams knock out event of the last American Summer Nationals held in Chicago in no small measure proved the efficacy of the rule.
Sitting South, Sabina Auken, three times world champion and much feared on the bridge table opened a weak two Heart (5-10 high card points). Janet doubled with 15 HCP with four cards of spades and balanced distribution, a typical double of weak 2 level bid. Jim Mahaffey, a great American player passed and Colchamiro with 10 HCP, three cards of spades and four cards of Hearts faced the dilemma.
Wasting no time he applied his rule. His total came to 9 with 
K; Q and 10 and 4 heart cards, plus level two and quickly passed. The decision resulted in a two trick gain of 300 and a swing of 350 as on the other table the East/West pair reached 3NT going one off on the lead of 
J. The full deal was:
Colchamiro has penned his experiences in Bridge in a book titled “How You Can Play like an Expert” (Magnum) and the rule of nine features in this publication. The book runs into three hundred pages and carries useful tips for the both the expert and for the one climbing up the ladder.
The deal mentioned above was reported by Phillip Alder in New York Times.