hi
... image 1 : that is a dimension based on " the principle of maximum material " ( i don't know if this translation is ok ); those 2 diameters have to be as concentric as possible; should be crafted without re-chucking/re-clamping the part
... image 2 : it may be a tolerance relative to other entities, but i really have no clue, unless i see the drawing / kindly