How should I wear my Polar device to get the most accurate heart rate readings from the wrist? (Video tutorial)

Applies to: A370, Grit X Pro, Ignite, Ignite 2, Ignite 3, M200, M430, Pacer, Pacer Pro, Unite, Vantage M, Vantage M2, Vantage V, Vantage V2, Vantage V3