Optical comparitors are stock in trade in the machine world. Depending on sophistication level, they may use pre-programmed, or CAD downloaded files as dimensions and tolerances as an example, and compare finished parts with those parameters. For PCB's, they are useful in much the same way but other inspection methods most often take precedence. They may be used to determine features, feature locations, solder mask openings, pad sizes and locations, etc. Again, this equipment primarily is used when machine products are made as those turned on a lathe, milled, or otherwise metal machined or formed. Together with CMM's, they can just about measure any feature on any part or the whole part. CMM"s are the mainstay of the automootive industry as they are programmed too measure points across small to very large parts as, say, automobile fenders, doors, etc. With GD&T, observing Taylor's principle, gaging is more appropriate. I would like to see more of this mothodology used in the PCB world especially pertaining to test fixturing on fine pitch part pads and test points that are growing ever more small and scarce with the disappearance of real estate. MoonMan --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------