 This type of sundial is known as an equatorial sundial because the plane of the dial face is parallel to the Earth 's equatorial plane . Two primary examples of modified equatorial sundials are bowstring equatorial and armillary dials . Both of these modified equatorial sundials can be read year @-@ round on the same surface , regardless of whether the Sun is above or below the equatorial plane whereas a standard equatorial sundial changes sides with each equinox and is virtually unreadable near the equinoxes when the Sun is located on the equatorial plane . 
