THE HAND THAT IS DOING THIS: the object at the centre of this shot is being held, operated, read, aimed or handed over by {handler} right now, so {handler}'s hand — and as much of the wrist and forearm as the framing reaches — is in the frame, gripping or resting on that object exactly the way its real use requires. Match that hand to {handler}: its size, build, skin, age, grooming, sleeve and anything worn on it belong to that person and to no one else.