Tipping-bucket rain gauge
From AMS Glossary
tipping-bucket rain gauge
A recording rain gauge in which the water collected continuously drains through a funnel into one of a pair of chambers or buckets that are balanced bistably on a horizontal axis.
When a predetermined amount of water has been collected, commonly 0.25 mm (0.01 in.) of rain, the bucket tips, spilling the water and placing the other bucket under the funnel. An electronic switch is excited each time the bucket tips so that both rain rate and accumulation can be determined from the record of tips.