Narrative:

Shortly after level at FL370 ATC asked our altitude. We replied FL370. We then realized we had not changed our altimeters to 29.92 at transition; they were still at 29.64. We reset altimeters.

Google
 

Original NASA ASRS Text

Title: B757 FLT CREW HAS ALTDEV.

Narrative: SHORTLY AFTER LEVEL AT FL370 ATC ASKED OUR ALT. WE REPLIED FL370. WE THEN REALIZED WE HAD NOT CHANGED OUR ALTIMETERS TO 29.92 AT TRANSITION; THEY WERE STILL AT 29.64. WE RESET ALTIMETERS.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.