How to calculate a simple 1/40 graduated head for beginners 

Hello everyone today I will share how I calculate the graduated disc on the 1/40 graduated head, this graduated head will help a lot of work for the worker when he wants to evenly divide the intervals of the machined part such as gear milling, flange hole drilling, hexagonal milling, milling the shaft of the tooth . . . And there are many more things that can be applied, I will guide the simplest calculation for beginners to see how I share