Shadow stick sundials trace back to the Greek shadow stick called the gnomon, meaning "the one that knows." People observed that shadows grew shorter or longer depending on the time of day and used them to measure time. As the earth turns on its axis, the sun appears to move across the sky, and in the northern hemisphere the shadows it casts move clockwise. Because the earth's elliptical rotation does not allow the sun to rise and set at the same time and location, shadow sticks were not accurate clocks. People later discovered that angling the gnomon and aiming it north made a more accurate sundial. An analemmatic sundial is a horizontal sundial with a vertical gnomon and hour markers arranged in an elliptical pattern. Its gnomon is not fixed and must change position daily to indicate the time of day accurately, so there are no hour lines on the dial and time is read only on the ellipse. Like most sundials, it marks solar time rather than clock time. It is defined by the size of its ellipse, the latitude of its location, and the declination of the sun, which determines the daily gnomon position. In this human sundial, a person becomes the gnomon by standing on the stone for the current month, facing north, and casting a shadow toward the Roman numerals that form the clock. During daylight savings time, the result is an hour behind the actual time. This analemmatic sundial was built by Boy Scout Troop 447 and friends and family of Danta Natle, who planned, designed, and supervised its construction for his Eagle service project. More than 30 volunteers spent 159 hours over three days completing it, and its Roman numerals were made from recycled bricks from the trolley system that ran through Rockville from 1900 until 1935.