Take a close up picture of your ear with a business card placed against your cheek.
Watch this video to see how to correctly find the perfect size.
Drag the box to match the business card. Use the ( - and +) to size the box and use the rotation symbols to align. If your business card does not appear to align with the rectangle, you may need to retake the picture and make sure the business card is perpendicular to the lense.
Drag the respective oval sizing shapes over the ear canal and match the best size.