Manual rain gauges are commonly used. However, there are a number of important factors to be taken into account in order to ensure the reliability of the instrument and the rainfall data it collects. If you wish to compare these data to those recorded by a Sencrop gauge, the following points need to be taken into account:
The two rain gauges must be absolutely level, at the same height, in the same place, following the rules on the positioning of the station (referring to the article ‘How and where should I install my Raincrop station?’).
The machine used for comparison must have been certified by an approved organisation. According to the World Meteorological Organization, ‘for liquid precipitation \[...] an area \[of the collector] of 200 to 500 cm² will probably be found most convenient.’ Also ‘the collector should be designed to prevent rain from splashing in and out. This can be achieved if the vertical wall is sufficiently deep and the slope of the funnel is sufficiently steep (at least 45%).’
WORLD METEOROLOGICAL ORGANIZATION (WMO), 2018. Guide to Instruments and Methods of Observation. ISBN 978-92-63-10008-5. https://library.wmo.int/doc_num.php?explnum_id=10179.