I'M VERY NEW TO THIS WORLD AND ALL IT INTAILS I HAVE TAKEN PCDMIS 101, AND 201 ABOUT 6 MONTHS AGO NOW AND IM SELF TAUGHT ON GD&T SO THAT I HAVE A BASIC UNDRSTANDNG OF IT. MY QUESTION IS HOW DO I ALIGN MY PART ONCE EVERYTHING MEASURED AN IM READY TO DEMINSION.THIS COMMON DATUM [A-B] MORESPECIFICALLY IS WHATS CONFUSING ME ON MY ALIGNMENTS. BTW THE PART IS SITAUTED SO THAT [A-1,A- 2] ARE IN THE Z+ POSITION 
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You don't define datums for legacy dimensions, they are dependent on the current alignment. What version of PC-DMIS are you using? It will be much easier to do the majority of the GD&T shown on your drawing if you use the geometric tolerance command (or XactMeasure in versions prior to 2020 R2).
This one in particular will be extremely difficult to do correctly using legacy dimensioning...
You don't define datums for legacy dimensions, they are dependent on the current alignment. What version of PC-DMIS are you using? It will be much easier to do the majority of the GD&T shown on your drawing if you use the geometric tolerance command (or XactMeasure in versions prior to 2020 R2).
This one in particular will be extremely difficult to do correctly using legacy dimensioning...
You don't construct a BF circle, you add a 2D best-fit of the 3x Cylinders to the alignment command. So, for the A-B|C datum reference frame, you would level to the A-B offset plane and then click the "Best Fit... button. Then in the Best Fit dialog, you would select the 3 cylinders from the feature list, select 2D from the type drop-down, select the workplane that you previously levelled to from the "2D Plane" drop-down, select the type of fit you want (vector Min/Max), hit compute and then OK.
