GD&T and a Alignment question

[[Ca...]]

1.Do you interpret datum A at the top surface or at centerline of the part?

2.For Calypso base alignment, do you pick the most stable datum feature for rotation in space (doesn't have to be in order from datums A,B and C)

Edited August 21

[[Cl...]]

That top surface is the datum. I don't use datums for my BA unless that's all I have. I use the largest, longest features that I think would

make the most stable/robust alignment. In your case (assuming that's just a rectangular block) and depending on the width, I'd use -A- for the primary

(rotation in space). I have no idea what the other datums are if any? 

Rotation in space = Primary

Planar Rotation = Secondary

X/Y or Z origin = Tertiary

Edited August 21

[[Ma...]]

This is only one side used as datum as Clarke wrote.

For having it as centerline - or usually as symmetry of two planes of this distance you would need to have datum A callout EXACTLY where is dimension number of thickness.
In other words - triangle of datum A have to be at exact place as arrow of 1.00 ( just a little bit higher than now )

[[Ca...]]

 

Datums B and C here are centerline?

[[Ma...]]

According to drawing standards it should be symmetry - so in center. But with B i am not sure what is that (50) STK.

[[Ca...]]

Its 50mm stock material. What we get is what it is, we will not be machining the two sides of B.

[[Ma...]]

OK, so this should really mean symmetry of two planes - i believe it's wanted to have it machined at centers of a workpiece