Meteorological data requirements for natural processes modelling have been augmented in modern agrometeorology. Close to the traditional parameters such as air temperature, relative humidity, solar radiation, rainfall, wind speed, etc., we need to define other devices to estimate for example soil water evaporation or leaf wetness duration. Many models for epidemiological applications use leaf wetness duration (LWD) parameter for diseases appearance prediction or infection simulation. Any standard has been defined for this type of measurement; hardware characteristics (colour, shape, dimension) and signal output follow the individual approach of the manufacturer more than a recognized ideal prototype. In this paper we try to give a brief description of the available instrumentation with some comment on the use and leaf wetness data interpretation.