This french curve ruler is large enough to have great curves for armholes and sleeve heads.
It is also great for necklines and curved style lines.
This is a great help for patternmaking in combination with the Pattern Maker ruler.
That being said, you should never trust a curved ruler blindly. Always make sure the lines make sense and have the right organic flow. The ruler is a help and a guideline – not the perfect final solution for all lines.