Comparison of KNMI and Hellmann manual rain gauges

In this experiment we compared two types of (commercially available) Hellmann manual rain gauges (two of each type) with two variants of the KNMI manual rain gauges (two of each variant) plus one KNMI manual rain gauge in a WMO pit. The experiment took place on the KNMI test field in De Bilt lasting from January 2020 to October 2021. The difference between the KNMI reference gauge and the Hellmann gauges appeared small compared to intergauge differences. Part of these differences are due to deviations in the orifice areas of the gauges and deviations in the readings of the measuring cylinders. It is concluded that the Hellmann manual rain gauge is a good replacement of the KNMI manual rain gauge. In case of a replacement, it is advised to perform parallel measurements at representative locations in the Netherlands, with a duration of two years. Observers need extra instructions to perform the measurements with the Hellmann gauge.