SPD CLRNC IS UNDERSTOOD TO BE AN ALT CLRNC SO CLB WAS STARTED BY ACR.

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WE WERE ON A SHORT FLT AT 15000 FT. THERE WAS WX IN THE AREA AND MOST FLTS WERE EITHER DEVIATING OR ON VECTORS AROUND IT. ATC WAS VERY BUSY. WE WERE TOLD TO CLB TO MAINTAIN 'ONE SEVEN THOUSAND' FT AND GIVEN AN ALTIMETER SETTING. I REPEATED THE CLRNC BACK AS THE CAPT AND I BOTH HEARD IT. MY CAPT INITIATED A 1000 FPM CLB USING THE AUTOPLT. SHORTLY THEREAFTER; ATC TOLD US THEY WERE SHOWING US IN A CLB (WHICH WE WERE). I THEN TOLD THE CTLR THAT SHE HAD CLRED US TO 17000 FT AND THAT I HAD READ IT BACK. THE CTLR TOLD US THAT THE CLRNC WAS NOT TO 17000 FT BUT TO MAINTAIN 'ONE SEVEN ZERO' KTS. WE SLOWED THE ACFT AND WERE THEN GIVEN A VECTOR TO RESEQUENCE. AT NO TIME WERE WE IN CONFLICT WITH OTHER TFC; IE; NO TA'S OR RA'S FROM TCASII. IF INDEED WE WERE TOLD 170 KTS AND NOT 17000 FT; THEN WHY THE ALTIMETER SETTING? THAT IS SOMETHING WE ARE USED TO ASSOCIATING WITH A CHANGE IN ALT OR A HDOF. CORRECTIVE ACTION COULD BE TO PREFACE A SPD ASSIGNMENT USING THE WORD 'SPD' AS IN 'REDUCE SPD; MAINTAIN 170 KTS' AND NOT JUST 'MAINTAIN 170 KTS.' IT'S VERY EASY FOR THESE THINGS TO TAKE PLACE WHEN THINGS GET BUSY. HOWEVER; THAT IS THE REASON FOR THE READBACK. LISTENING IS THE KEY TO COM.