CAPT OF AN MLG ACR ACFT INADVERTENTLY SET THE WRONG VOR RADIAL IN THE FMC RESULTING IN BEING OFF COURSE BY 20 MI. ATC CTLR INTERVENED AND THE MISTAKE WAS CORRECTED.

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WE WERE DEVIATING AROUND WX N OF ORLANDO ON J53. WE WERE HDG 320 DEGS TO CLR WX TRYING TO THEN GO OVER CRAIG AND THEN THE ARR INTO ATL. WE WERE INSTRUCTED TO FLY 270 DEGS AND INTERCEPT J119 TO TAYLOR THEN DUBLIN AND THE ARR. THE FO; WHO WAS FLYING; CHKED THE CHART. J119 WAS 186 DEG RADIAL. I SAID THAT'S 306 DEGS INBOUND. HE SAID OK AND WE TURNED INBOUND. CTR SAID AGAIN FLY 270 DEGS AND INTERCEPT J119 INTO TAYLOR 'DID YOU GET THAT?' WE REPLIED 'WE WERE WORKING ON IT.' THEY SAID HE HAD TFC OVER GAINESVILLE SBOUND AND HE NEEDED US ON J119. WE ROGERED; CHKED THE CHART AND YES 186 DEGS OUT IS '006' IN -- NOT '306' DEG. WE RESET AND GOT IN J119. COULD HAVE BEEN PREVENTED BY BETTER BASIC MATH. HOWEVER; WITH WX DEV GOING ON AND NOT TOO SURE HOW FAR AWAY J119 WAS; I FIGURED TOO QUICKLY AND FO DIDN'T CATCH IT. MAYBE CTR COULD HAVE SAID 'INTERCEPT J119 YOU ARE 20 MI E OF IT' OR SOMETHING LIKE THAT TO TAKE AWAY SOME OF THE URGENCY OF THE SIT. ALSO; WITH A GLASS COCKPIT; ONE GETS OUT OF THE HABIT OF SETTING COURSES ON AIRWAYS.