During a visit to the Manchester Museum of Science and Industry, we noticed a lovely clock where the digits had been replaced with mathematical formula. A great idea for getting children to think about numbers.
However, it is too small to be of use in classroom for us and, frankly, was probably too hard for the children so we decided to make our own. We used Powerpoint to create the different representations for each digit and created a different set for each term ranging from straight forward calculations to the names of 2D shapes. To make it a clock we bought a clock mechanism for a ridiculously cheap price from the internet (like this one). Hey presto - one mathematical clock for the classroom. If you want to use it, please feel free to use the PDF from our Dropbox.