A system for automatically forming stacks of cartons for feeding a magazine for supplying cartons to a packaging machine includes a primary support on which the stacks of cartons are formed, and a secondary support for temporarily receiving a series of the cartons thereon as a previously formed stack of cartons is removed from the primary support. The antenna includes: a base radiation portion, a connecting portion, a first radiation portion and a second radiation portion. The highest intensity sample is identified from the stored samples and this is compared against a predetermined threshold. This makes the method less sensitive to variations in cell size and morphology than prior art methods for cell counting, such as Coulter counting.