THE REPROGRAMMING REQUIRED BECAUSE OF A ROUTING CHANGE ENDS IN A TRACK DEV ON THE IDALE RNAV 1 DEP FROM LAS; NV.

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FO WAS FLYING THE IDALE1.HEC DEP. APCHING ANDYY FIX; LAS DEP CTL CLRED US DIRECT BOACH FIX AND ISSUED FURTHER CLB. I ENTERED THE FIX IN THE FMC AND THE ALT IN THE MCP. FO CONFIRMED BOTH. ATC LATER GAVE US A TURN APPROX 25 DEGS L FOR DIRECT BOACH. WE BOTH REALIZED FMS WAS COMMANDING A COURSE FOR DIRECT HEC. I BELIEVE THAT AT THE TIME THE CLRNC FOR DIRECT BOACH WAS RECEIVED; I MUST HAVE SEEN IT WAS LINE-SELECTABLE IN THE FMC. IN THE SLIGHT DELAY I TOOK TO SELECT IT; WE PASSED OVER ANDYY FIX. BOACH WOULD THEN BECOME THE '2L' BUTTON ON THE FMC. I; HOWEVER; MISTAKENLY PUSHED 3L ANYWAY; WHICH WOULD HAVE SELECTED HEC AS THE NEW 'DIRECT TO' FIX. THIS WAS EXECUTED; AND NEITHER PNF NOR PF REALIZED IT. IN THE FUTURE; I WILL BE MORE COGNIZANT OF EXACTLY WHAT IS IN THE FMC BEFORE I EXECUTE; AND BACK IT UP WITH THE DISPLAY ON THE EHSI. SUPPLEMENTAL INFO FROM ACN 565868: I WAS PF AND WATCHED AND CONFIRMED THAT CAPT LINE SELECTED BOACH TO TOP OF LEGS PAGE AND HIT ENTER. I TURNED ACFT TO GO DIRECT AND CALLED FOR LNAV. A FEW MINS LATER; ATC SAID WE WERE NOT GOING DIRECT. I HAVE NO EXPLANATION AS TO HOW THE FMC CHANGED FROM DIRECT BOACH TO HEC. I DID NOT SEE IT ON THE MAP PAGE ON THE NAV DISPLAY BECAUSE I WAS ON THE 10 SETTING.