Thank you for your reply @Grace !
I use the Esmod method for sewing patterns. Here are the instructions of the method:
- sleeve crown length = armhole depth - its 1/8th
To find the depth, Esmod request to join the front and the back and drawing lines :
I also found this formula:
armhole depth = (“2” + “4” ) /2
I tested it on a hand-drawn pattern: I do not have the same result as with the traditional method. I will continue my research. If I find a reliable formula, I will share it with you. 