Pressure gauge (9)
I believe the answer is:
barometer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pressure gauge</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for barometer that I've seen before include "Weatherglass" , "One measures pressure" , "It measures air pressure" , "One showing pressure" , "Pressure indicator" .)