A B727 PIC FAILS TO FOLLOW THE DRYHEAT SID AFTER RECEIVING AN AMENDED CLRNC RTE CHANGE AT PHX.

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FLT 1 HR LATE; NO PDC. AT PUSHBACK; HAD TO CALL FOR CLRNC. FILED SID WAS FOR 'ST JOHN' SID; CLRED FOR 'DRYHEAT' SID. PUSHED BACK; PERUSED SID DURING TAXI OUT FOR RWY 8L. FLT FILED FROM PHX TO ATL (EBOUND); CLRED FOR IMMEDIATE TKOF. FLEW TO PXR THEN OUTBOUND ON 075 DEG RADIAL TO A DME; THEN TRANSITIONED TO 070 DEG RADIAL TO GILAA INTXN. ABOUT 1 MIN LATER; DEP SAID CLRED TO INTERCEPT 070 DEG RADIAL; THEN IMMEDIATELY ANOTHER DEP VOICE (SUPVR?) ASKED IF THIS WAS FIRST CLRNC TO INTERCEPT 070 DEG RADIAL. I CHUCKLED; SAID 'YES;' AND THAT 'IT WAS SURPRISING SINCE WE WERE ALREADY ESTABLISHED ON 070 DEG RADIAL.' I WENT BACK TO SID TO SEE THAT IT CALLED FOR TURN TO 100 DEG HDG AT A DME OFF OF 075 DEGS; FOR ALL DEPS; EVEN EBOUNDS. AT HDOF TO ZAB; I APOLOGIZED AND TOLD DEP I MISREAD SID DEP PROCS. NO COMMENT. REMAINDER OF FLT UNEVENTFUL. THERE WERE NO ACFT CONFLICTS DUE TO MY MISTAKE. NO TCASII TFC OBSERVANCE. NO TURNS REQUIRED BECAUSE OF CONFLICTS. I BELIEVE MY HASTE TO MAKE UP TIME; AND MISREAD OF SID CAUSED PROB. HOWEVER; THE DEP INSTRUCTIONS ON SID MAKES THIS PROC VERY AMBIGUOUS AND EASY TO MISINTERP.