RG13(H) uses a pulse-based tipping-bucket mechanism to produce a contact closure every time it receives a predetermined quantity of rainfall: 0.1 mm (0.004 in) or 0.2 mm (0.008 in).
The body and funnel of the gauge are aluminum alloy. The septum ring at the top gives an aperture of exactly 400 cm2 (62 in2).
The tipping-bucket mechanism is mounted inside the body on a cast aluminum-alloy base that has fixing slots, 3 leveling screws, and a spirit level. The mechanism consists of a divided bucket pivoted at its center. Rain collects in the upper half. When this is full, the mechanism tilts and discharges the collected water, so that the other half of the bucket can start filling.
A siphon device is fitted to the base of the funnel to control the rate of flow into the buckets. By ensuring a constant flow rate into the tipping bucket, calibration is made easier and accuracy improved.
The heating turns on when the temperature drops below +4 °C (+39 °F).
