The ClimaVue 50 is a microclimate sensor, so you should position it to be representative of the climate relevant to the research questions you are asking. FAO56 gives specific guidelines to the positioning and field size of sensors. If you intend to use the sensor for reference ET, follow those guidelines. Refer to the following: http://www.fao.org/docrep/X0490E/X0490E00.htm.