i love this system, it is extremely intelligent and one of the best things you can have if you love to exercise. You simply plug it into your compatible nike shoe and it can calculate many useful things while you're exercising. It plugs into your iPod nano, which you then have to put into your pocket, or like I do put it into my ipod nano arm band so that it doesn't thrash about in my pocket, and I can listen to music while it calculates all the measures of my exercise. It calculates things like the time you were running for, the distance you travelled and the pace you were travelling at and one of the most useful stats especially when you're on some sort of diet, the amount of calaries that you burnt while you were exercising. This has to be one of the best inventions from apple, who are swiftly creating items to suit every individuals needs, with extremely advanced and effective products. Thanks Apple!