CAPT OF ACR MLG ACFT INADVERTENTLY PROGRAMMED THE FMS WITH THE WRONG DME DISTANCE FOR A XING RESTRICTION RESULTING IN NOT COMPLYING WITH THE RESTRICTION.

Narrative

ACR FLT FROM ATL TO DAB. DURING CRUISE ALT FROM ATL TO DAB; ABOUT LAKE CITY; FL; MY COPLT HAD TO LEAVE THE COCKPIT FOR THE RESTROOM. ABOUT 1 MIN AFTER HE LEFT; WE STARTED TO GET LIGHT TO MODERATE CAT. I ASKED ZJX FOR FLT CONDITIONS AND GOT A LOWER ALT. ABOUT THIS TIME I TURNED ON THE SEAT BELT SIGN; AT SAME TIME A FLT ATTENDANT CAME UP TO INQUIRE ABOUT THE TURB. THE BELL RANG AGAIN FOR THE FO TO COME BACK UP. I WAS MAKING A PA TO THE PAX REGARDING THE TURB; I.E.; REMAIN SEATED; ETC. DURING ALL THIS; OR IN THE MIDDLE OF ALL THIS; I GOT A XING RESTRICTION 20 OR 30 DME N OF CRG FOR FL240. I READ BACK 20 DME AND ENTERED IT IN THE FMS DSCNT PAGE. MEANWHILE; THE COPLT IS BACK IN THE LOOP AND WE ARE DSNDING; PASSING FL260 FOR FL240 AT 25 DME N OF CRG. AT THIS TIME THE COPLT BRINGS UP THE POINT THAT ALL MONTH ON THIS LEG THE XING RESTRICTION WAS 30 DME; NOT 20 DME. I AGREED WITH HIM. WE WERE CLRED TO THE NEXT CTLR BY THEN AND NO MENTION AS TO THE XING DME. I READ BACK 20 DME; PUT 20 DME IN THE FMS BUT I'M STILL NOT SURE WHAT WAS CORRECT.