How do you calculate the cutting angle of an open-ring segment?

How do you calculate the cutting angle of an open-ring segment?

Answer: (360° – (segments * gap)) ÷ segments ÷ 2. 
Example: 24 open segment ring with 4 degree gap = (360 – (24 * 4) ÷ 24 ÷ 2 = (360 – 96) ÷ 24 ÷ 2 = (264 ÷ 24) ÷ 2 = 11 ÷ 2 = 5.5°