There's no need to purchase a rain gauge if you looking for pure functionality. Take any clear container with a flat bottom. The mouth of the container should be the same size as the walls. The pasta sauce jar I used has just a slightly smaller mouth than the sides but it's close enough to give me a relatively good gauge of how much rainfall occurred. Take a ruler or tape measure and place inside the jar against the bottom and mark off your measurements. Place it in your garden or yard away from building and with nothing hanging overhead other than clear sky.