Plane line point vs plane plane plane

All 3 Datums are large enough to pick up a reliable plane, then I align them as planes. If one side is small I may choose to do a line instead, but only if it is not the Primary Datum.
According to the ASME standard, a Plane-Line-Point is proper. The only issue with this when using a CMM is that ASME follows the rules of measuring on a surface plate, which a CMM would not be able to replicate easily, if at all. Datum A should rest on the 3 highest points on a theoretically perfect plane, and that plane would be your Datum. Datum B would rotate and origin it's edge on the 2 highest points on it's surface against a theoretically perfect and perpendicular plane in relation to A, and the 2 points would essentially be datum. The third datum would then rest it's furthest point against a theoretically perfectly plane perpendicular to A and B, and that point would be Datum C. (See the ASME standard for reference pics.) This is easy with hard gauges, but with the CMM you cannot guarantee that the areas you probe will be the high points. You could scan all of the surfaces, create a tangent plane and a bunch of if/else statements and flow control to try and mimic a hard gage as best as possible, or you can use 3 planes and do what the majority of people do. Is it proper? No. Is it more repeatable? Almost always yes.

Thank you! This is the sort of answer i was looking for. Something relateable back to some sort of industry standard. I am decently familiar with the ASME standard (obviously not as well as i should be) but that is where i will start. The man is as bullheaded as they come, im not intrested in whos right or wrong, im only interested in insuring things are as accurate and repeatable as possible. My word doesnt mean much to him but hopefully if i can reference some industry related guidlines among other things we can come to an agreement. I appreciate your input. Thank you again!

Thank you! This is the sort of answer i was looking for. Something relateable back to some sort of industry standard. I am decently familiar with the ASME standard (obviously not as well as i should be) but that is where i will start. The man is as bullheaded as they come, im not intrested in whos right or wrong, im only interested in insuring things are as accurate and repeatable as possible. My word doesnt mean much to him but hopefully if i can reference some industry related guidlines among other things we can come to an agreement. I appreciate your input. Thank you again!