Abstract: To reduce time spent at the check-out of a self-service shop, each customer is provided with an electronic recording unit mounted on the receptacle used to collect items for purchase. The unit has a memory store for data identifying the items collected. The prices and gross weights of the items are summed, e.g. by extraction of data from a data store in the unit or from data input from a bar code on the items themselves. The collection of items is weighed as a whole at the checkout for comparison of the measured weight with the computed sum of the gross weight of the individual items.