By default, seams have a straight corner. You can however create a rounded corner when you want to take a seam corner that is straight and make it round. This can be useful for example when you want to have a slit in your pattern and you want to add extra seam allowance.
Icon & Location
To create a rounded seam corner:
Open up your pattern.
Add your seams.
To make the corner of the seam rounded, in the Toolbox, select Round Seam Corner.
Select the point where you want to start the rounded corner.
While holding down your mouse, drag until you reach the point of the seam and then let go of your mouse.
The Round Corner dialog appears.
In the Radius field, enter the radius angle of the corner.
The corner is rounded as follows: