Can't interpret GD&T callout

In this day & age you have to take GD&T with a grain of salt because designers (especially recent engineering grads from fancy colleges) who use it tend to have little practical understanding  how it works in the real world.

Here looks like they are concerned about drilling those holes perpendicularly to A. Datum modifier is there for datum shift nothing else. 

I would use 1st B (upper left) as my xy origin point and 2nd B as datum C for clocking. Use trig to figure out the angle & compensate in the alignment window. 

I never bother with datum shifts; the machinist doesn't care much either. 

If you aren't sure about the datum scheme I would advise going to the designers & ask them for the assembly CAD or colored drawing so you yourself build the datum scheme per assembly precedence. Then go thru with them what their reasoning is for this GD&T or that GD&T. If that's futile go to the machinist/CAM programmer & inquire what is their order of operations. Then go to your boss & explain what you will do. That way it ain't on you. 

In this day & age you have to take GD&T with a grain of salt because designers (especially recent engineering grads from fancy colleges) who use it tend to have little practical understanding  how it works in the real world.

Here looks like they are concerned about drilling those holes perpendicularly to A. Datum modifier is there for datum shift nothing else. 

I would use 1st B (upper left) as my xy origin point and 2nd B as datum C for clocking. Use trig to figure out the angle & compensate in the alignment window. 

I never bother with datum shifts; the machinist doesn't care much either. 

If you aren't sure about the datum scheme I would advise going to the designers & ask them for the assembly CAD or colored drawing so you yourself build the datum scheme per assembly precedence. Then go thru with them what their reasoning is for this GD&T or that GD&T. If that's futile go to the machinist/CAM programmer & inquire what is their order of operations. Then go to your boss & explain what you will do. That way it ain't on you. 

MattR said:

In this day & age you have to take GD&T with a grain of salt because designers (especially recent engineering grads from fancy colleges) who use it tend to have little practical understanding  how it works in the real world.

Tru dat...  

MattR said:

I never bother with datum shifts; the machinist doesn't care much either. 

I thought I was the only one.  Good Lord, I swear engineer types are just trying to pad their drawings by adding too many modifiers, incorrect Datums, or just plain wrong datums.