Cat's eye sundial
The sand glass was the tool used most often by "ninja" for establishing the time of day. However, they also used another method for this purpose. The cat's eye sundial is a method for telling the time by the aperture of a cat's eye. The eyes of a cat look fully round and open during the twilight periods at daybreak and sunset. They reduce in size to a near-oval shape between 8:00 and 16:00, and even more so at between 10:00 and 14:00. At 12:00 noon they become extremely narrow almost needlelike in a straight line. The "ninja" used this type of sundial because they knew the properties of cat's eyes very well. As seen above, the "ninja" were experts at various martial arts and made free and full use of their knowledge including artillery, astronomy, meteorology and the ecology of animals and plants.