A glass tumbler
A plastic tube (you will get this in any hardware shop)
Some bubble gum
Place the ruler in the glass tumbler and hold it against one side.
Using the cellotape, tape the ruler on the inside of the glass tumbler. Make sure the ruler markings can be seen through the side of the glass tumbler.
Place the plastic tube into the glass tumbler. Make sure that plastic tube does not touch the bottom of the glass tumbler and tape it to the ruler.
Pour water into the glass tumbler until it is half-full.
Chew a piece of bubble gum until it is soft.
Carefully suck some water halfway into the tube.
Use your tongue to trap the water into the tube. You can also use your thumb to hold the water.
Quickly stick the piece of chewing gum on the top opening of the plastic tube and seal it.
Mark the water level in the plastic tube and notice the water level mark a few hours later.
How does it work?
What you had created is a barometer. A barometer is a device used to measure atmospheric pressure. Atmospheric pressure is the weight of air that surrounds the earth. Atmospheric pressure is different in different altitudes and on higher grounds like hills and mountains and lower plains. If the water level rises up the plastic tube, it means there is more atmospheric pressure at a given time and if the water level falls in the plastic tube there is low atmospheric pressure at a given time.