A B737-300 WAS DISPATCHED WITH #4 LEADING EDGE SLAT POS INDICATION SYS DEFERRED INOP WITH A PREVIOUS DEFERRED ITEM ON 'B' HYD SYS PRESSURE INDICATION INOP. THIS WAS IN CONFLICT WITH THE MEL.

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DURING TAXI OUT THE FLC EXPERIENCED AN INDICATION PROB WITH THE #4 LEADING EDGE SLAT; DEFERABLE PER THE MEL WITH CHKS ACCOMPLISHED TO ASSURE PROPER OP. PART OF THE MEL CHK IS TO CONFIRM 'B' SYS HYD PRESS AND TEST BOTH STALL WARNING SYS. THIS AIRPLANE HAD ANOTHER DEFERRED ITEM ON THE 'B' SYS HYD PRESSURIZE INDICATOR RPTED AS INOP. THE PLACARD FOR THIS ITEM STATED IN PART THAT 'B' SYS PRESSURE WAS TO BE VERIFIED BY USING THE HYD BRAKE PRESSURE INDICATOR WHICH WAS FUNCTIONING NORMALLY. ALL CHKS WERE ACCOMPLISHED AND THE AIRPLANE DEPARTED AFTER I HAD CONFIRMED WITH ANOTHER CTLR IF THIS ALTERNATE MEANS OF VERIFICATION WAS SAFE. I COULD SEE NO REASON WHY IT WAS NOT SAFE AS THE PLACARD SPECIFICALLY STATED TO USE THIS INDICATOR FOR VERIFICATION OF SYS PRESSURE. MY MAIN CONCERN IN FILING THIS RPT IS UNDER THE HUMAN FACTORS PORTION; IT WAS XX00 AND NEARING THE END OF DUTY SHIFT; I WAS TIRED AND UNSURE CAUSING ME TO BECOME CONFUSED WHEN READING THE INFO. THE FLC WAS IN A HURRY AND DID TAKE SOME PROMPTING TO SLOW DOWN SO WE COULD ASSURE A SAFE DISPATCH. I PLAN TO DISCUSS THE WORDING OF THE MEL WITH OPERATIONAL ENGINEERING GROUP TO CLARIFY AN ACCEPTABLE MEANS IS INSERTED.