The other end will be off the jar. When the glue has dried tape some paper to the wall and move your barometer so that the pointer you made points to the center of the paper. Use a pencil to mark the spot. Check it daily and notice if the pointer has moved up or down. Up means good weather, down means stormy weather.
Barometric pressure is a measure of the air pressure.
If the air pressure is high it usually means nice weather. You can predict this by noticing when air pressure presses down the balloon and causes your straw pointer to rise. Low pressure usually indicates storms and your pointer will fall. Land Snails Drifted Along Streams after Floods.