If precision is considered, I would say that 0.0 kg is not the same as 0.0 mg.
Whether something is actually zero depends on how closely you are looking.
For vectors, if the magnitude is (for example) 0.0 m/s, I allow them
to omit the direction as it is undefined. The units are always a good
idea.
Mike
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Michael Porter
Colonel By Secondary School
Ottawa, Ontario, Canada