I feel like a Pirate with this Barometer

I highly doubt that pirates actually used barometers, but barometers are used to measure the atmospheric pressure.

The following picture shows a barometer that is filled with liquid. 

We made homemade barometers that would measure the atmospheric pressure. The following picture shows how the barometer worked. We used a small glass bowl with a balloon over the top with a straw cut to a point tapped on top                                     of the balloon.                                         When there was high atmospheric pressure, the ballon would be pulled into the glass and the straw would rise; when there was low atmospheric pressure, the balloon would inflate and the straw would point downward. 

The following is the data collected from the calibration of the homemade barometer.

The following graph depicts the data that we collected.