DEPARTING FROM PHX FLT CREW OF MD80; ORIGINALLY CLRED VIA CHEZZ RNAV FROM DEP; FAIL TO SELECT PROPER NAV MODE WHEN RECLRED VIA STANFIELD DEP.

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DEPARTING RWY 7L. ATC FLT PLAN: CHEZZ2.DRYHT.J74.TXO.UKW7.DFW. REVISED ATC CLRNC: CHEZZ2.DRYHT DIRECT TXO.UKW7.DFW. ROUTINE PREFLT INCLUDING A TKOF BRIEF OF DEP TO BE FLOWN. CHEZZ2 SID WAS AN RNAV DEP. FO AND I DISCUSSED PROCS OF THE SID; DECIDED TO SELECT NAV/RADIAL SWITCH TO NAV AND BOTH NAV DISPLAY TO MAP MODE. DURING TAXI OUT TO RWY 7L; A REROUTE WAS ISSUED. NEW RTE: STANFIELD ONE DEP; CIE TRANSITION. WE REVIEWED STANFIELD ONE DEP AND THE NEW RTE. GFMS WAS UPDATED WITH STANFIELD ONE DEP. WE BOTH HAD PXR VOR FREQ SET -- INITIAL DEP HDG OF 078 DEGS WAS ALSO SET. BUT BOTH OF US FAILED TO RETURN NAV/RADIAL SWITCH TO RADIAL. DISCUSSIONS WERE ALSO MADE REGARDING NOTIFYING DISPATCH OF OUR NEW RTE ONCE WE WERE AIRBORNE. FO'S TKOF WAS NORMAL AND ONCE AIRBORNE; ASKED FOR HDG SELECT OF 078 DEGS TO 1550 FT AND THEN FLEW 075 DEG HDG. SHORTLY AFTER; TWR SWITCHED US TO DEP FREQ. AS I ENDED MY INITIAL CONTACT WITH DEP CTL; I OBSERVED 4.0 DTG ON MY NAV DISPLAY AND MISUNDERSTOOD FOR 4.0 DME FOR PXR VOR. (NAV DISPLAY WAS ACTUALLY READING 4.0 DTG TO WAYPOINT PXR 4 DME.) I REMINDED FO OF OUR POS OF PXR VOR 4.0 DME AND A TURN TO 190 DEG HDG WAS REQUIRED. FO INITIATED THE TURN TO 190 DEG HDG. AS WE BANKED PAST 120 DEG HDG; DEP CTL QUESTIONED OUR HDG AND PROCEEDED TO INFORM US THAT WE HAVE MADE OUR TURN TOO SOON. DEP CTL CLRED US TO FLY A NEW HDG AND WE COMPLIED IMMEDIATELY. AT THIS MOMENT; FO AND I NOTICED OUR ERROR OF INCORRECTLY READING 4.9 DTG TO WAYPOINT PXR 4 FOR 4.0 DME OFF PXR VOR WITH NAV/RADIAL SWITCH TO NAV. I IMMEDIATELY COMMUNICATED WITH DEP CTL OF OUR ERROR. DEP CTL MENTIONED NO CONFLICTING TFC AND SHORTLY AFTER; CLRED US DIRECT TO CIE VOR. REMAINDER OF FLT TO DFW WAS NORMAL. SUPPLEMENTAL INFO FROM ACN 602182: BOTH OF US FAILED TO RETURN NAV/RADIAL SWITCH BACK TO RADIAL. HE OBSERVED 4.0 DTW ON THE NAV DISPLAY AND ADVISED ME TO TURN TO THE 190 DEG HDG. I GLANCED AT THE NAV DISPLAY TO VERIFY THE DME BUT SINCE MY SETUP WAS THE SAME I ALSO SAW 4.0 AND INITIATED THE TURN.