Duane,
Go into GEOMeasure Customization, select more (top right) and make sure "Position tol with 1-3 datums" is checked. If this is off the current coordinate system is always used and the datum's are used for MMC only. With it on, if there are no datum's defined it will use the current coordinate system. If you define a datum reference you must use features that relate to the 6 degrees of freedom. In other words, the primary datum can not be a two dimensional feature. You should also use the maximum inscribed or minimum circumscribed calculation to avoid a calculation error. You should use this on all datum features. The book even suggest that when you measure your datum plane that you set the base plane to the least squares calculated plane and then translate it to the furthest point of the plane. This is done to avoid error equal to the form of the datum feature. It is all listed pretty clearly on page 8-38 in the Operation section of the GEOMeasure manual. So I guess to answer your initial question there are four that I know of. Relative to the current coordinate system, relative to a primary datum, relative to primary and secondary datum's, and relative to primary, secondary and tertiary datum's. I hope this is what you was looking for.

Best regards,


Terry W. Prather

Dexter Axle P13 - Albion, IN