The basic unit in the Maya calendar was one day, or k'in. This was multiplied by twenty to form a winal. The next unit, instead of being multiplied by 20, as called for by the vigesimal system, was multiplied by 18 in order to provide a rough approximation of the solar year
(hence producing 360 days). This 360-day year was called a tun. Each succeeding level of multiplication followed the vigesimal system.