A positional tolerance defines a zone within which the center, axis or center plane of a feature of size is permitted to vary from the true (exact) position. Basic dimensions establish the true position.
In the example shown, the center of the holes must lie within circles 0f 0.5mm diameter when the holes are at 10.25mm diameter.
As the diameter of the holes increases to 10.5mm diameter, the tolerance zones increase proportionately to 0.75mm diameter.
The tolerances, in this example, apply to the center distance between holes as well as the location of these features as a group from the datum planes (A-B-C).