So here is the part loaded against the primary datum "D" (clamped to the left block) and against the secondary datum "A" (loaded against angle plate in rear) Then I have a 1-2-3 block resting on tertiary datum "B".
Notice the measurement on the height gage. I was worried about my measurement, because if the corner has an edge break on it, it wont be to the theoretical sharp corner.
Hopefully this makes more sense?
This pic shows where the demon is measuring datum "B" from.