From Glossary of Meteorology
The most common type, the triple register, records wind direction and speed, duration of sunshine, and amount of rainfall (sensed, respectively, by a contact anemometer, Marvin sunshine recorder, and tipping-bucket rain gauge). The register consists of a rotating, clock-driven drum on a helical axis, a separate pen for each element, and the actuating mechanism for the pens. Double registers are also used. Multiple registers of this type are becoming obsolete.