The invention relates to a mass comparator comprising: a weighing chamber (16); a draught shield (18, 20, 22) surrounding the weighing chamber (16); a climate module (34) removably arranged in the weighing chamber (16); a processor (32) arranged in the mass comparator; a data input unit arranged on the mass comparator; and a data transmission path via which data can be exchanged between the climate module (34) and the processor (32), said processor (32) being designed in such a way that, based on the density of the item to be weighed, the processor can identify the air buoyancy of at least the test item and/or the buoyancy correction factor from the air pressure, the air humidity, and the air temperature in the weighing chamber (16). The invention also relates to a climate module for electrically coupling to a mass comparator in a detachable manner, said climate module (34) forming a complete sub-assembly and comprising an air pressure sensor (62), an air humidity sensor (54), and an air temperature sensor (52), as well as a portion of a data transmission path via which data can be sent to a processor external to the climate module. The invention further relates to a method for operating a mass comparator having a weighing chamber (16) separated from the surrounding area by a draught shield, and in which chamber an air pressure sensor (62), an air humidity sensor (54), and an air temperature sensor (52) are arranged, wherein said sensors (52, 54, 62) are coupled to a processor (32), and wherein an item to be weighed, in the form of a test item (B), and at least one reference weight (A) are weighed, said method being characterised by the following steps: identifying the air pressure, the air humidity and the air temperature in the weighing chamber (16), using the sensors (52, 54, 62); inputting the density of the item to be weighed into the mass comparator, the mass of which item is to be determined; identifying the air buoyancy of at least the test item (B) and/or the buoyancy correction factor from the air pressure, the air humidity, the air temperature and the density of the item to be weighed; and determining the corrected, conventional weight value of the test item (B).