Atmospheric pressure measurer (9)
I believe the answer is:
barometer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">atmospheric pressure measurer</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for barometer that I've seen before include "Atmospheric pressure measurer" , "It checks state of sky" , "Weatherglass" , "Weather forecaster" , "Pressure gauge" .)