With 10 days to Christmas, it might be a good idea to look how the advent calendar came about.
19th century German Christians started to develop traditions in timekeeping towards Christmas. In 1851, the first prototype of the Advent calendar appeared—German Protestants started to hang one picture per day on the wall, until Christmas Eve, thus totalling 24 pictures. Catholics in the same period put in one straw per day in the nativity scene, fulfilling the same timekeeping function.
The first printed Advent calendar appeared at the start 20th century—in 1902, an evangelical publisher in Hamburg pioneered the Advent clock, with the numbers 13 to 24 on its face. In 1903, the modern Advent calendar was born—with a Munich publisher launching an Advent calendar with the 24 doors we usually see today. Children would cut one door out each day and paste it somewhere else.
The tradition spread to Britain and Scandinavia, and in 1934, the first Advent calendar in Sweden is published by the girl scouts.
Over the years, the Advent calendar developed into diverse formats, including calendars with hidden chocolate pieces, Advent candles with 1 to 24 painted on their side, as well as gigantic calendars taking the form of a Christmas tree or a building.
In 1957, inspired by the Advent calendar then still published by the girl scouts, Sveriges Radio pioneered the Advent calendar programme, followed by the public service television channel SVT in 1960. Advent calendar programmes usually follow the form of a 24-episode series, and children would follow the storyline throughout December until Christmas Eve. This has spread to other Nordic countries, thus becoming a unique Nordic Christmas tradition.
Sources in the respective Wikipedia articles in German and Swedish