Whether you are a recreational or serious swimmer it's good to be able to monitor your progress in the water. Up until recently, if you wanted to work out how far you'd swum in any one session you would have to count up the lengths and multiply them by the length of the pool – a process fraught with complications especially, if like me, you tend to forget to keep tally after a few lengths. However, here's a gadget that automatically works out how far you've swum – and does far more clever stuff besides. Read on to find out more.