There is described an efficient and simple method of billing a client for using a computerized numerical control machine. The invoice amount to be billed is based on at least one trajectory of at least one axis during operation, on a volume of a stock removed from a work piece during operation, and on a processing time information related to working on the work piece. One concept of the method therefore is a pay-per-use concept relating the added value created by the computerized numerical control machine to the invoice amount.