Making a pattern with a perfect neckline requires using a gape or contour dart.

This technique is also used for other openings, e.g. armholes and cut out details. In this tutorial I explain the reasoning for contour / gape darts.

I show you using a bust circle, and also show you in practice how to do this when pattern cutting.

It's not essential to draw the circle every time you do this, but it's great to understand WHY you're doing the gape dart that you are.

You can read more about it on my Gape Dart Blog.