B777 CREW GAVE THE WRONG TIME ESTIMATE FOR ENTRY INTO OCEANIC AIRSPACE.

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AT APPROX AB15Z; I CALLED SHANWICK OCEANIC FOR AN OCEANIC CLRNC. I CHKED THE FMC FOR AN ESTIMATE FOR XING 52 N 15 W. THE FMC WAS ESTIMATING AC36Z. IN THE PAST; I HAVE READ THE ESTIMATE DIRECTLY OFF THE FMC WHEN REQUESTING A CLRNC. THIS TIME MY RELIEF PLT HAD WRITTEN ON THE TRACK MESSAGE THE PROPER ORDER OF THE INFO TO GIVE SHANWICK ON CALL UP FOR THE CLRNC. NEXT TO ENTRY POINT HE HAD WRITTEN 52/15 EST.... I RECHKED THE FMC WHICH WAS STILL ESTIMATING AC36Z AND THEN PUT DOWN AD36Z; WHICH IS THE ESTIMATE I THEN GAVE SHANWICK. I WAS NOT AWARE OF THE TIME ERROR UNTIL PASSING 52 N 15 W AT AC38Z AND SUBSEQUENTLY GETTING A CALL FROM SHANWICK INFORMING ME OF THE MISTAKE. AFTER RECEIVING CLRNC; I RECORDED ON THE MASTER FLT PLAN THE ESTIMATE OF AC36Z THAT I THOUGHT I HAD GIVEN TO SHANWICK. I THINK THAT DEVIATING FROM MY NORMAL HABIT OF READING ESTIMATES DIRECTLY FROM THE FMC CONTRIBUTED TO THE ERROR. BY WRITING THE 15 W ESTIMATE ON A SEPARATE PIECE OF PAPER; I OPENED MYSELF UP TO TRANSCRIBING AN INCORRECT NUMBER. NO TFC CONFLICT OCCURRED BECAUSE OF THE TIME ESTIMATE ERROR.