The ASME standard assumes that geometric tolerances apply to the full length (or depth) of the toleranced feature; the projected tolerance zone modifier clarifies that the tolerance zone applies a specified length outside of the toleranced feature.

Un-projected Example

Consider the case of a threaded or press-fit hole that lines up with a clearance hole

Technically, the part meets the positional requirement of its detail drawing, but the mating component cannot assemble because the bolt meets interference at the top corner of the clearance hole:

Projected Example

The projected tolerance modifier was created to indicate that the threaded hole's position tolerance is projected beyond the hole. It is actually a “borrowed” tolerance zone: it’s the same tolerance zone as the clearance hole of the mating part.

Notice that the tolerance is related to the datums, so the direction of projection is dependent on where datum A is.

Also notice that the number after the projected modifier indicates the length of projection is determined by the thickness of the mating part (or parts), which in this case is 14 mm.