MECHANIC CALLED OUT TO LOOK AT A FORWARD CARGO DOOR FOR DENTS ON B737-900 AIRCRAFT; USED THE LENGTH MEASUREMENT INSTEAD OF THE WIDTH MEASUREMENT; WHEN HE APPLIED THE W/Y FORMULA IN THE SRM FOR DETERMINING ALLOWABLE DAMAGE.

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ON ACFT X I WAS CALLED OUT TO LOOK AT A FORWARD CARGO DOOR FOR DENTS. MY MEASURES WERE 1.1 INCH BY 2.5 INCHES BY .040 INCH DEEP. PER THE SRM; MY WIDTH/DEPTH MUST BE 30 OR MORE. I USED THE WRONG MEASUREMENT IN MY FORMULA. (I USED 2.5 INCHES/.040=62.5) MY FORMULA SHOULD HAVE BEEN 1.1 FEET/.040-27. I PLACED THE DENT ON MAINT HISTORY RATHER THAN DEFERRED ITEM REF SRM ALLOWABLE DAMAGE SECTION. I HAVE ALREADY CLOSED THE MAINT HISTORY AND OPENED THE CORRECT DEFERRED ITEM IN REF WITH SRM ALLOWABLE DAMAGE SECTION. NEW GENERAL SRM WITH MAX WIDTH VERSUS CLASSIC MINOR AXIS. JUST USED THE WRONG MEASURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE NEXT GEN B737-700/800/900 STRUCTURAL REPAIR MANUAL (SRM) USES THE LETTER 'W'; MEANING WIDTH; FOR THE DAMAGE CRITERIA FORMULA W/Y; TO DETERMINE IF THE AIRCRAFT DAMAGE REQUIRES IMMEDIATE REPAIR; OR CAN BE DEFERRED UNDER CERTAIN CATEGORIES. THE 'Y' FACTOR REPRESENTS THE DEPTH OF THE DENT. REPORTER STATED THE CLASSIC B737-300/400/500 SRM'S CONTINUE TO USE THE LETTER 'A' FOR THE WIDTH FORMULA WHEN DETERMINING THEIR A/Y DAMAGE CRITERIA. HE JUST USED THE LENGTH MEASUREMENT; INSTEAD OF THE WIDTH; FOR THE DAMAGE CALCULATIONS.