ACR PIC ACCEPTS ACFT WITH MULTIPLE MEL REQUIREMENT DEFICIENCIES.

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THE ACFT; A B-757; WAS RELEASED TO ME WITH THE APU INOP AND ALSO THE R PNEUMATIC DUCT PRESSURE GAUGE INOP. THE APU INOP MADE IT NECESSARY TO START THE R ENG AT THE GATE; THEN XBLEED START THE L ENG AFTER PUSHBACK. THE PREVIOUS CREW HAD NOTED IN THE ACFT LOGBOOK 'R DUCT PRESSURE GAUGE APPEARS TO FUNCTION NORMALLY.' MAINT ASKED ME TO EVALUATE IT ON OUR FLTS FROM PIT-LGA-CLT-PIT. IT DID IN FACT FUNCTION NORMALLY; HOWEVER; I'M NOT CERTAIN THAT I WAS LEGAL TO ACCEPT THE ACFT AND START ENGS WITH THE DUCT PRESSURE GAUGE ON MEL. THERE WAS NO LEGAL WAY FOR ME TO MEASURE DUCT PRESSURE WITHOUT GOING TO THE MAINT STATUS PAGE ON THE EICAS; WHICH ISN'T A PROC PLTS NORMALLY UTILIZE. THE FACT THAT DEST WX WAS AT MINIMUMS AND RWY CONDITIONS WERE ICY; AND PAX BOOKINGS WERE FULL AND THEN SOME WERE ALL ITEMS OF CONCERN. I DID WHAT I HAD TO DO TO OPERATE THE FLT SAFELY. HAVING MULTIPLE; UNRELATED ITEMS ON MEL WAS DEALT WITH; BUT IT MAY NOT HAVE BEEN LEGAL; SINCE THAT PARTICULAR COMBINATION OF MALFUNCTIONS IS NOT COVERED IN OUR TRAINING OR MANUALS.