AN ACR MLG CREW FLEW AN ACFT WITH ONLY 1 OPERATIVE AIRSPD INDICATOR.

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I PREFLTED OUR ACFT AND FOUND THAT THE FO'S AIRSPD INDICATOR WAS INOP. I CALLED MAINT AND PUT THE DISCREPANCY INTO THE LOGBOOK. OUR ACFT WAS DESIGNED TO USE EFIS; BUT OUR COMPANY NEVER HAD THEM INSTALLED. IN THE EQUIP BAY; THERE ARE EFIS COMPATIBLE PARTS. OUR MAINT PERSON TOLD US THAT HOUSTON MAINT CTL OK'D AN MEL WHICH ALLOWED US TO OPERATE THE ACFT. ONE OF THE RESTRICTIONS TO THE MEL SAYS; 'A) EFIS SPD TAPE DISPLAYS ARE INSTALLED AND OPERATE NORMALLY.' WE POINTED THIS RESTRICTION OUT TO OUR MAINT PERSON. HE TOLD US HE WOULD CHK WITH HOUSTON MAINT. HE CAME BACK A SHORT TIME LATER AND TOLD US; 'THEY SAID THE MEL WAS OK.' WHEN WE GOT TO FLL; THEY TOLD US IT WAS NOT AND CHANGED THE AIRSPD INDICATOR. IT WOULD HELP IF THE MEL WAS WRITTEN FOR PEOPLE AND NOT LAWYERS. SUPPLEMENTAL INFO FROM ACN 258356: THE MEL INDICATED THAT IT WAS OK TO PROCEED. I WAS NOT SATISFIED WITH THE MEL AND ASKED THE MECH TO CALL MAINT IN HOUSTON. ON ARR AT THE NEXT STATION; I WANTED A RECONFIRMATION ON THE AIRSPD INDICATOR. HOUSTON MAINT TOLD HIM THAT THE MEL DID NOT RELATE TO THIS ACFT CONFIGN.