The Chinese Calendar assumes a prime meridian of 120 degrees East. This means that a day (or rather, a nychthemeron, aday and a night) is taken to run from midnight Beijing standard time (BST) to the next midnight BST. This is in contrast to the Common Era Calendar, where a nychthemeron runs from midnight Greenwich Mean Time (GMT) to the next midnight GMT. The time difference between Beijing and London is eight hours, so nychthemerons (or nychthemera) in the Chinese Calendar begin eight hours earlier than days in the Common Era Calendar.