The Double-Traversing Weighing Rain Gauge is also known as the Double-Tracking Weighing Rain Gauge, and the Universal Weighing Rain Gauge.
Inside the unit is a continuous graph which records rainfall time and intensity over a 24-hour period. The red and white metal panels surrounding the gauge act as wind barriers, thus allowing precipitation to fall relatively unhampered into the mouth of the gauge; they quiet the air directly above the collector funnel.
The collector funnel is 14 inches in diameter; below the collector is a catch bucket. The weight of the bucket (empty) is zeroed out on the scale. When rain water fills the bucket, the weight of water depresses the scale causing a pen arm to rise on the continuous graph across which it tracks an ink line.
As mentioned, the scale is connected to a pen arm which rises as the scale lowers at a rate equivalent to rainfall intensity. The pen arm records time of occurrence and intensity of precipitation on graph paper (accurate to 1mm of precipitation). The graph paper is able to hold up to 24 hours of continuous precipitation data. Note the continuous chart on the right & the pen arm near its base. Follow that pen arm back, and you can faintly see the scale. On top of that scale is a bucket, which appears to be filled with enough water to suggest that a total of about a quarter of an inch of rain has fallen here; as indicated by the height of the pen. This photo was taken by the National Weather Service Office in Albany, New York.
Any increase (in the ascent of the ink line) indicates precipitation occurrence. If this ascent ends and the ink line remains level, this indicates a “dry period” during the storm system; a time period when rainfall has stopped.
The motor under the cylinder around which the chart is wrapped must be manually reset every 7 days by hand cranking a small handle. Most weighing rain gauges use spring-loaded motors. There are some that run on battery-powered motors as well.
~ Steve Woodruff and Devin Lussier