Float-type rain gauge
From AMS Glossary
float-type rain gauge
A class of rain gauge in which the level of the collected rainwater is measured by the position of a float resting on the surface of the water.
This instrument is frequently used as a recording rain gauge by connecting the float through a linkage to a pen that records on a clock-driven chart.
Middleton, W. E. K., and A. F. Spilhaus 1953. Meteorological Instruments. 3d ed., rev., . Univ. of Toronto Press, . 121–122.