We find it so easy to write down any number using our ten digit system that we do not realise how long it took to invent or appreciate how difficult it was. In this day school we shall look at number systems devised by different civilisations around the world. Among other things we shall investigate Babylonian cuneiform, find out why we have 60 minutes in an hour, watch Archimedes counting grains of sand and visit both India and the Yucatan peninsula in Central America. However we shall not dwell entirely in the past and we shall see why computers prefer to do things differently. There will be some practical activities to help you engage with the ideas.