Question: How do I draw a 45 cm diameter circle on the leather ?
Option 0: Cut a 22.5 cm string with scissors, fix one end on the string  on the leather with you left hand and grab the other end of the string with your right hand while holding a pencil. By tensing up the string, draw a circle with your right hand.
Option 1: Cut a 22.5 cm string with scissors, fix one end on the string  on the leather with you left hand and grab the other end of the string with your right knee while holding a pencil. By tensing up the string, draw a circle with your right knee.
Answer: 0