Abstract: An improved apparatus for and method of measuring the mass of the contents of a product is described, in which the mass of the contents of the product is relatively small compared to the mass of the entire product. The products are sequentially conveyed to an inspection station where preferably a predetermined portion of the volume of the product (which includes at least a portion of the volume of the contents) is substantially instantaneously irradiated with a beam of radiation and preferably only scattered radiation from the contents of the product thus irradiated is detected to provide an electrical signal whose magnitude is representative of the mass of the contents of the product. The products can then be sorted in accordance with the measured mass of their contents.