(Kelly of the Clue Crew gives the clue from a lab.)  Stretch a balloon over a glass, secure with rubber bands, then place a straw on top & you have a simple version of this device that measures air pressure
Well, then tell 
me why, using the same bowing motion, you get one design with ... What 
happens if you do the same with a rubber band stretched between ...... How does 
this cottage barometer work, and does it actually measure the barometric 
pressure?