Place the phone under your nipple. Make sure you are measuring the widest part (just above where the nipple meets the areola)

Measure your Right breast’s nipple, linear, from side to side. Adjust the orange segment until the lines are aligned with your nipple’s widest part. Take a note of its size in cm.

Measure your Left breast’s nipple, linear, from side to side. Adjust the orange segment until the lines are aligned with your nipple’s widest part. Take a note of its size in cm.