This is a handy skill to know and easy to do. Hopefully I can make it look as easy as it is. I am making here a 3" to 4" branch.
For the purpose of this post I am just making a paper template, but you can make a template with any suitable material. Plastics, cardboard or thin steel sheet are great because you can keep them for future use.
To start you will need a piece of A3 or bigger size paper. I have used a piece of butchers paper here On this you need a line through the center and a line square to this down the bottom.
On your centre line, draw two circles.
The top circle is 4" and the bottom cicle is 3". Place a line square to centre through your branch circle. With your compass set at the same radius as your branch circle (1.5")
bisect your cicle like this.