The imaginary line on the Earth’s surface stretching from pole to pole through the Pacific Ocean which, by international agreement in 1884, marks the beginning or ending of a day. The line approximately follows the meridian of longitude 180°, bending where necessary to avoid cutting through land. To the east of the line, the date is one day behind the west of the line. On crossing this line in a westerly direction the calendar must be put forward one day, while if it is crossed in an easterly direction the calendar is put one day back.