A red wire or thread that crosses the earth plate and heaven dial at 90-degree angles is the "Heaven Center Cross Line", or "Red Cross Grid Line". This line is used to find the direction and note position on the rings. A conventional compass has markings for four or eight directions, while a luopan typically contains markings for 24 directions. This translates to 15 degrees per direction. The Sun takes approximately 15.2 days to traverse a solar term, a series of 24 points on the ecliptic. Since there are 360 degrees on the luopan and approximately 365.25 days in a mean solar year, each degree on a luopan approximates a terrestrial day.