Ambient+Weather+Rain+Gauge+Accuracy

How do I test the accuracy of a digital rain gauge?
To determine the accuracy of a digital rain gauge, you need to know the surface area of the funnel.

If the rain gauge has a rectangular inlet:

Area = length x width

If the rain gauge is circular:

Area = ( π x d 2 ) / 4, where d is the diameter of the rain gauge.

The calculation is as follows:

Total Rain = Water Volume / Area

Example
If the rain gauge is rectangular, and the surface area of the inlet is as follows:

Area = 11 x 5 cm or 55 cm 2

If you pour in 100 ml of water (or 10 cm 3 ) SLOWLY (over a 10 minute period), one would expect the rainfall to equal:

Total Rain = 10 cm 3 / 55 cm 2 = 0.18 cm or 18 mm of rain (+/- the accuracy specification of the rain gauge).

Since 1 mm = 0.03937 inches, the total rain (inches) = 18 x 0.03937 inches/mm = 0.71 inches.

Take into account the resolution of the rain gauge.

If the resolution is 0.04 inches for example, the measurement would be 0.04 inches/tip x 17 tips = 0.68 inches.

FAQs
1. **My rain gauge is under reporting**. > There is an excellent discussion on rain gain modifications here: [|Rain Gauge Modifictions] 2. **My rain gauge is over reporting.** Make certain the pole is not vibrating during windy conditions, causing false readings
 * Make absolutly certain the rain gauge is level! If not perfectly level, the tipping mechanism will not work properly and under report rain.
 * Make certain there are no obstructions in the funnel and tipping mechanism. In heavy downpours, the rain droplets can "bounce" out of the rain gauge.