A B737-300 WAS DISPATCHED AND OPERATED IN NON COMPLIANCE WITH NON STANDARD FUEL FLOW INDICATORS CALIBRATED IN KGPH. REQUIRED PPH INDICATORS.

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DURING CRUISE FLT WHILE DOING A TREND CHK ON ENGS; NOTICED THAT FUEL FLOW READINGS WERE UNUSUALLY LOW. LOOKING VERY CAREFULLY AT THE GAUGES WE NOTED THAT THE FUEL FLOW (FF) WAS IN GPH INSTEAD OF THE REQUIRED PPH. THE BLUE LETTERING ON GAUGE; WAS APPROX 1/8 INCH TALL ON BLACK BACKGROUND; MAKING IT VERY HARD TO READ. WE CONVERTED GPH TO PPH AND CAME UP WITH THE STANDARD FUEL FLOW. WE MONITORED FUEL FLOW AND FUEL QUANTITIES; AND CONTINUED TO OUR DEST UNEVENTFUL. AT DEST NOTIFIED MAINT ABOUT PROB. MAINT STATED THAT THEY CHANGED FUEL FLOW GAUGES BEFORE OUR FLT. FLC HAD NO INDICATION OF THE CHANGE FROM THE MAINT LOGBOOK. CORRECTIVE ACTIONS WOULD BE TO ALERT PLTS OF THE FUEL FLOW GAUGE CHANGE; AND BE CAREFUL TO NOTE UNITS OF MEASURE ON ALL GAUGES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT DURING THE FLT THE BLUE NUMBERS BECAME HARDER TO READ AND THEN NOTICED THE FUEL FLOW WAS A LOT LOWER THAN NORMAL. THE RPTR SAID AFTER A CLOSER LOOK IT WAS OBVIOUS THE WRONG INDICATORS WERE INSTALLED BEING CALIBRATED IN KILOGRAMS PER HR INSTEAD OF LBS PER HR.