by sketching in the extra construction line and adding relation(s) and dimension(s).
You can use 3 points to dimension an angle. Pick the top end of the vertical construction line, the center of the semicircle, and the center point of the slot.
Very good Jerry I only found out yesterday that you could do this. Its on my one to remember list.
Good suggestion, Jerry.
However ( I don't now why) I get the right results if I make the Smart Dimension in this order:
1) Center of the semicircle
2) Top end of the vertical construction line.
3) Center point of the slot