I discuss the basis of an arithmetically dominated interdisciplinary project on stamping envelopes, which involves the following skills and knowledge areas: weighing, estimating weights, a little history and geography, economics and politics, marketing, accountancy and information processing, interpreting and consulting tables, deciding between alternatives by balancing cost against speed of delivery, making up face values under various constraints, awareness of knock‐on effects of industrial action, and the planning and budgeting of mail runs. I concentrate on Post Office material, but also provide ample reference to, and analogy from, other public utilities and business perspectives.