Trace back and front separate, then adjust the length to 15cm above knee or desired measurement.
On front, highlight underbust line and draw the button closure this way:
- draw a line parallel to center front, inwards by 2cm
- draw another line parallel to center front, outwards by 2cm.
This way you identify a section 4cm wide that is button stand (i.e. the space for buttons and buttonholes). Cut through the line to separate front from button stand.