That is precisely what the geometric statement means: "...position tolerance within a circle." It reduces scrap and part rejection if it is done right. It allows for a bonus tolerance over the bilateral (square) tolerance zone. A square zone is limited. A circle has more area where the center of the drill is allowed. One thing that is missing is the tolerance applies to a Maximum Material Condition. The statement should have a circle with an "M" inside. And it usually, but not always, has a tertiary datum specified. There are a few places to get good books on this. One is http://www.engineersedge.com/GDT_Training.htm Regards Bob Wilson CID Electro-Mechanical Designer SpectraSensors, Inc. 972 N. Amelia Ave. San Dimas, CA 91773 800-619-2861 x239 www.spectrasensors.com -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Donald Kyle Sent: Monday, July 10, 2006 8:10 AM To: [log in to unmask] Subject: [TN] Geometric Tolerance 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.+ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------