The concept is simple, Velcro (or Velcro-like) materials are used to attach the fitness tracker to your ankle. I knew when ordering that it might be undersized (and need modification) but to be honest the hook part is a cheap plastic thing, not the usual velcro hooks and it barely connects to the fuzzy part of the ankle strap. However, the piece of velcro-like material over the mesh where the device is meant to be hidden is sewn so tightly that you can barely open the pocket to insert the device (which needs to be removed from a regular armband for it to work) . . There are a lot of things in it that don't work. I ended up designing my own.
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