It uses Archimedes' principle of water displacement to show how many inches of rain fell.
The tube rises as the water fills the copper collection cylinder. The blue plastic tube is marked upside down -- one inch at the top, and 5 and half inches at the bottom.
Since the tube magically rises as rain fills the cylinder, the lower rainfall inches are at the top, so you can see an inch of blue rising from the cylinder from inside the house when an inch of rain has blessed your garden.
When there has been no rain, there is no blue tube sticking up -- it's housed inside the copper cylinder.
It needs no mounting on a post or stake. It's a tabletop version, so it will sit on the patio table, or maybe on the top of the stone wall around the patio. How easy is that?
Okay, I'm ready for some rain to test whether Archimedes knew what he was talking about or not.
This is Archimedes. He was Greek, and he lived 250 years before Christ.
I like to think that ancients and ancestors and people who came before me are with me in the garden every day. I need all the help I can get.