Answer:
I do not know!!!!:(
If you are drawing an isometric drawing by hand (pencil / paper), go purchase a 30 / 60 / 90 triangle (don't forget to use a straight edge to align the triangle).
If you are using CAD, change your snap to Isometirc and use CTRL + E to rotate between the planes (top, left, right).
Also use crating to help you draw curves!!