DC10-30 CREW HAD TROUBLE SETTING A 'DIAL-A-FLAP' POS THAT WAS CLOSE TO A FIXED FLAP GATE.

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THIS IS ONE OF THOSE SITS OF 'LIVE AND LEARN.' HOPEFULLY NOTHING WILL COME OF IT. FLT STARTED AT EWR WITH AN OAK DEST. AS WE TAXIED OUT OF EWR; WHEN THE FLAPS WERE SELECTED TO 20 DEGS; THE FLAP HANDLE WENT TO THE 22 DEG DETENT (FIXED STOP/GATE); AND THE FLAP INDICATOR WENT TO 21 DEGS. WE CYCLED THE FLAPS 2 TIMES WITH SAME RESULTS. WE TALKED ABOUT IT; THE FLAPS APPEARED ALL NORMAL OTHER THAN THE 1 DEG DIFFERENCE IN INDICATION. WE WERE #1 FOR TKOF; SO WE ELECTED TO TAKE OFF. UNEVENTFUL FLT TO OAK. ONCE PARKED AT OAKLAND; I MADE AN ENTRY INTO THE ACFT MAINT LOGBOOK; INDICATING THE DIFFERENCE (1 DEG) AMONG THE DIAL-A-FLAP SELECTOR; THE FLAP INDICATOR AND THE 22 DEG DETENT. BRIEFED THE ACFT MECH WHO MET US AT THE PLANE. IT WAS ONLY ON A SUBSEQUENT FLT THAT WE DECIDED (AND REMEMBERED) THAT WE COULD HAVE REFED TO THE MEL. MUCH TO OUR SURPRISE; THE DIAL-A-FLAP WAS LISTED AS A 'FLAG' ITEM; WHICH MEANT WE SHOULD HAVE RETURNED TO THE EWR RAMP AND HAD IT REPAIRED PRIOR TO TKOF. THE MEL STATED THE DIAL-A-FLAP MUST 'OPERATE NORMALLY.' WHAT DOES 'NORMALLY' MEAN? IS IT EXACT -- IN OTHER WORDS; IF WE SELECT 17.9 DEG FLAPS AND IT INDICATES 17.8 OR 18.0 (ON A 20 YR OLD AIRPLANE); DOES THAT MEAN IT IS OUT OF TOLERANCE? I REALLY BELIEVE THERE SHOULD BE MORE SPECIFIC EVIDENCE IN THE MEL (WHEN I TOLD THE MECH ABOUT IT IN OAK HE SAID; 'OH YEAH; WE SEE THAT A LOT'). SO IT MUST BE COMMON. THERE WERE SOME OUTSIDE FACTORS THAT CONTRIBUTED TO MY DECISION TO CONTINUE: 1) NEVER SEEN THIS PROB BEFORE; UNFAMILIAR WITH IT. 2) 20 YR OLD AIRPLANE. POSSIBLE WEAR ON MOVING PARTS; THEREBY 'SLOPPY' MOVEMENT OF DIAL-A-FLAP HANDLE. 3) TALKED ABOUT IT WITH OTHER CREW MEMBERS. NONE HAD A PROB OR THOUGHT OF THE MEL UNTIL NEXT FLT; OR FELT IT UNSAFE IN ANY WAY WHATSOEVER. 4) WE WERE #1 FOR TKOF. DID NOT FEEL IT NECESSARY TO RETURN TO GATE (WE WERE WRONG). 5) ON BOARD WAS A COMPANY CHK AIRMAN; ADMINISTERING A CHK RIDE TO ME. HE SAW WHAT WE DID; NEVER SAID ANYTHING LIKE 'ARE YOU GUYS SURE YOU WANT TO DO THIS?' AFTERWARDS DURING THE DEBRIEF (BUT PRIOR TO THE NEXT FLT WHERE WE AS A CREW REALIZED IT WAS A FLAP ITEM) I ASKED THE CHK AIRMAN FOR INPUT REGARDING THE FLAP HANDLE AND HE SAID 'I SAW WHAT YOU DID; OK WITH ME.' 6) ONLY AFTER HE LEFT; AND WE WERE ON A SUBSEQUENT FLT; WE RESEARCHED IT AND FOUND OUT THE REQUIREMENT TO RETURN TO GATE AT EWR. 7) I FOLLOWED UP WITH ACFT MAINT AND CONFIRMED THE ACFT HAD BEEN REPAIRED BEFORE IT FLEW AGAIN. NEXT TIME; I WILL CHK THE MEL AT THE MOST MINOR MECHANICAL PROB ON THE GND. MY CREW AND I DEBRIEFED THIS EXTENSIVELY. WE KNOW WHAT TO DO BETTER NEXT TIME.