{HEAD ~ The heart rate sensor} 305 is a robust blood volume pulse sensor positioned about the center of {TAIL ~ the forehead} and a rechargeable or replaceable battery module 307 is located over one of the ears 
{ HEAD ~ The heart rate sensor } 305 is a robust blood volume pulse sensor positioned about the center of { TAIL ~ the forehead } and a rechargeable or replaceable battery module 307 is located over one of the ears
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