dnobie,
I do not particularly like the way ASME shows you how to work out positional tolerances. It is easy to work out from first principals.
You have a 1/4" bolt. Presumably, there is a nut at the opposite end, and we can assume the bolt is located precisely at nominal. It occupies a space Ø.250". Your clearance holes must not encroach on this.
Your hole's smallest acceptable diameter must be located accurately enough that it does not occupy the Ø.250" diameter. If your smallest hole is Ø.280" in diameter, it can safely shift .015" off of nominal position, for a positional tolerance of Ø.030".
POSHOLE = MINHOLE - MAXBOLT
If the bolt is a screw, i.e. it is located in a tapped hole, you must account for the positional tolerance of the tapped hole. A 1/4" screw located inside Ø.015", occupies a space of Ø.265". Your Ø.280" hole must clear this, and can therefore shift a maximum of .0075" for a positional tolerance of Ø.015".
POSHOLE = MINHOLE - MAXSCR - POSSCR
If you are clamping something thick, you should account for the tapped hole being at an angle by enlarging your assumed tapped hole positional tolerance, or by applying a projected tolerance zone to it.
JHG