Don,

First, you should be looking at IPC-2615, Printed Board Dimensions and
Tolerances for the most current information. It was created to embrace
the principles set forth in Y14.5 as they apply to printed boards. The
IPC-D-325 was created prior to the latest release of Y14.5 and does not
fully reflect current symbolics.

I looked at both your references and could not find where they indicate
an X and Y to be added to the control frame. X and Y clearly indicate
bi-lateral tolerances. The control frame, minus your X and Y references,
would clearly indicate a diameter of true position of 0.005 inch. The
Datum references are usually used to relate this control frame to
another feature control frame such as a datum.

Regards,

Gary Ferrari
FTG Circuits
Director, Technical Support
860-350-9300



Donald Kyle wrote:
> We are having a little debate here as to the interpretation of a
> Geometric statement evolving the tolerance of holes on a PCB.
>
> The geometric statement reads from left to right:
> Position (symbol)
> Diameter (symbol)
> .005 (tolerance)
> X (datum)
> Y (datum)
>
> Some say that this statement means a positional tolerance zone within a
> circle.
>
> Others say that this is just another way of stating a bilateral
> tolerance zone within a square.
>
> How do you interpret this?
>
> If you have IPC-D-325A you can read about this on page 28 and
> appendix B for more information.
>
> Because I don't know how to insert a geometric symbol for POSITION
> and DIAMETER you will need to use your imagination here.
>
>  Geometric      Geometric       Tolerance       Datum
>  Symbol for     Symbol for                      Reference
>  Position       Diameter
>        __             __                   .005                 X      Y
>
>
> Thanks for your time
>
>
> Donald Kyle C.I.D.+
>
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