A G159 CAPT NEGLECTED TO RESET HIS ALTIMETER; PASSING FL180; DURING CLBOUT.

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AFTER DEPARTING FTW; WE WERE FLYING THE WBOUND SID AND BEING STEP-CLBED BEHIND ANOTHER ACFT. PASSING FL180; I CALLED FOR THE FL180 CLBING CHKLIST AND WE BEGAN TO ACCOMPLISH IT. THE DEP ALTIMETER WAS 30.62 AND JUST AS I BEGAN TO RESET TO 29.92; THE FLT ATTENDANT CAME INTO THE COCKPIT AND BEGAN TO ASK SEVERAL QUESTIONS FROM THE PAX. I CONTINUED TO TURN THE KNOB WHILE TALKING TO HER. WHEN I LOOKED BACK AT THE ALTIMETER ALL I CHKED WERE THE LAST 2 DIGITS WHICH READ .96 AND THEN MOVED THE KNOB TO OBTAIN .92. UNFORTUNATELY IT WAS 28.92; WHICH I MISSED. THE CTLR CONTINUED STEPPING US UP WITHOUT ANY ALT STOP TO FL290. AT FL280; THE COPLT NOTICED THE DISCREPANCY BTWN OUR ALTIMETERS AND I DISCOVERED MY ERROR. I BEGAN TO LEVEL OFF AND THE COPLT ASKED THE CTLR TO CONFIRM OUR ALT AS FL290 AND THE CTLR RESPONDED 'CLB TO FL310.' I AM NOT REALLY SURE IF WE WERE EVER AT THE WRONG ALT BUT ITS CERTAINLY POSSIBLE; AND A SERIOUS MISTAKE. AS FOR WHY IT HAPPENED; OBVIOUSLY I ALLOWED MYSELF TO BE DISTR FROM THE TASK I WAS TRYING TO ACCOMPLISH. ADDITIONALLY; THE LARGE DIFFERENCE BTWN DEP AND ENRTE ALTIMETERS MEANT THAT I KNEW I WOULD HAVE TO TURN THE KNOB QUITE A BIT AND CONTINUED TO TURN WHILE DISTR AND MORE IMPORTANTLY FAILED TO CHK MY WORK. THE LESSON TO BE LEARNED HERE IS AN OLD ONE -- THE AIRPLANE COMES FIRST; PAYING ATTN TO YOUR JOB WILL REALLY CUT DOWN ON STUPID ERRORS AND I SHOULD HAVE ASKED THE FLT ATTENDANT TO WAIT UNTIL I HAD FINISHED THE TASK AT HAND. YOU CAN BET I LEARNED A LESSON AND SOME HUMILITY.