Make a fist and rotate your hand around. Watch the area. On my forearm, two muscles diverge and make a harsh edge that slashes through the middle of the region. That will not be good for a flex long term. That are not meant to be flexed, they are made on flexible PCB. The solder joints and chip are delicate. We suggest the watch area for the same reason watches are worn there: it is stable, convienent, and experiences a minimum of movement.
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