Was at the Doc's this morning and the nurse asked a question that I can't answer.
Her young son at school was given a balloon a straw and bottle to measure the pressure.
What happens when the pressure is Low and when it is High pressure please to the balloon?
I think that is all the boiy had but do not know if there was water involved or not.  The Mother does not know either as think the child did not asorb what he was told and therefore could not relay it to her.
If anyone can help here please that would be appreciated as she is ringing me tonight.

I would think you need water in the glass bottle - say 3" in bottom, lay bottle on its side carefully with the water, or sloping so you can get some baking soda in the neck without getting into the water, put straw to bottom sticking out the top even but with a cork plug holding it and sealing the straw and into the bottle, add an empty balloon over the top of the bottle carefully - still horizontal - tie off tight with string etc.  Then pick up and gently shake.

Balloon will enlargen with pressure and water level will go up the straw and even into the balloon.  It will stabilise somewhere or you may need to do it again with less baking soda!!

Now leave upright for weather to interact.  With high pressure, it will try and compress the balloon smaller forcing the water down the straw back into the bottle.

In a Low pressure system, the balloon will relax and expand and the water will rise up.  Opposite to what we think perhaps, but it would be a barometer.

Not sure how to do it without the cork or baking soda (Enos would do as well...)

Sounds fun anyway...  could be messy too..

Option 2 without the baking soda - place glass bottle in freezer with some water in the bottom standing upright.  Let it freeze overnight.  (Or empty and add water in the morning with straw, bung and balloon)

Next day, add the straw and also a balloon quickly over the end and seal off - still need the cork plug with straw glued into it (or sealing well against the straw). Don't push the straw and bung in too far yet - just touching the ice so can push it in through the balloon later as it melts (or straight into water if using method 2).  Don't hold the bottle with your hands - it will warm it up too soon.  OK to touch it once balloon is sealing the end.

This will operate the same as above.

Perhaps I have got this way too complicated - I don't know...

Thank you very much you kind people and will pas the information on to her when she rings.  Wil salsa print off as having to go back to the Doc's on Wednesday again.
I have also learnt something too.
Much appreciated once again as did not do these sorts of things when I went to school many many years ago.

Actually figured for my one, you can get those larger balloons with fatter necks tht would fit on a bottle easily, just blow it up a bit before hand holding air in with borrowed fingers, while stretching neck over bottle.  Best to start mine during a high pressure period around 1030HPa and to add food colouring dye to the water.  Can use a cable tie to hold a balloon onto a jar or bottle.

You can mark the straw out in cm's.  10mBar or 10 HPa (going from 1000HPa to 1010HPa) is equivalent to 9.1cm of water (91mm).  So slight air pressure changes will be seen easily and measured.  Ie going from 1000mbar to 1030mbar is 3 x 9.1 = 27.3cm  (engineers always work in mm or m, a cm is not a scientific SI measurement (the standard system of metric units) but is good for rulers and sort of relates to inches).  I always see that as 273mm...    A full range would be from 980Hpa to 1035HPa or 55HPa => 5.5 x 91mm =  500mm - a very tall bottle and straw!!! But you could use a plastic tube and a certain tall alcohol bottle... LOL!  Needs to be emptied first!

When blowing warm air into the baloon, it will cool down and shrink lifting up some water into the straw to start with as it reaches stability.  As the Low pressure comes over, it will suck up water up the tube and the balloon will get bigger...

Where has the one gone with the drawing of the bottle and straw balancing please - as wish to print off these to take to the Doc tomorrow.