The invention relates to a method, a system and a computer program product for ascertaining a plant property of a useful plant in a field, wherein external data concerning the useful plant are stored in a memory unit, wherein a measurement device ascertains a raw measured value relating to at least one plant property, and wherein a calibrated or corrected value for the plant property is ascertained on the basis of the raw measured value taking account of the external data from the memory unit.
