Stone pencils, or sekihitsu, were instruments for writing, marking or drawing made of natural minerals such as chalk, graphite, soapstone, and others. According to the Shoninki shinobi manual, shinobi would use them to take notes and make marks. This would be done when walking along unfamiliar mountain paths. A shinobi could also knot grasses to make markings that map where he has been. If they come to a dead end, they would go back to where the path began and take another path. According to the Giyoshu military manual, secret marks could be used to communicate with allies.