When purchasing materials, the unit of purchase is the multiple of individual items in which the purchase is expressed. If hand towels are packed in sleeves of 50 and there are 20 sleeves in a box, the unit of purchase could be a single hand towel, a sleeve of 50, or a box of 1000. Purchasing problems occur if the unit of purchase and the unit of sale are not aligned or are expressed in ambiguous terms. For example, if I order hand towels and in the quantity column of the purchase order the quantity is stated as 50, the supplier has to decide whether I want one sleeve of 50 hand towels, or 50 boxes of hand towels, i.e. 50,000 hand towels. Stating the unit of purchase as ‘50 boxes of 1000’ would reduce the ambiguity. See also Unit of Sale.