The beautiful image above (click to zoom) represents the month of September in the Très Riches Heures du Duc de Berry, a book of hours from the 1400s. In the background of the main picture is the Château de Saumur, with its height exaggerated (almost doubled). For comparison, below is a modern photograph of the château (by Kamel15) stretched vertically ×2:
The foreground of the main picture shows the grape harvest. At the top is a complex calendar. On the inner track, around the chariot of the sun, in red and black numerals, are the days of the month. On the outer track, in red and blue numerals, is a zodiacal calendar, showing the last days of Virgo and the beginning of Libra. Adjacent to the inner track are blue letters which relate to the 19-year Metonic cycle. Combining those letters with an appropriate table will show the phases of the moon for a given year.
The manuscript uses the Hindu-Arabic numerals first introduced to Europe by Fibonacci in his Liber Abaci of 1202. They are not quite the same as the ones we use today:
It is interesting to compare those digits with the ones in this German manuscript of 1459 by Hans Talhoffer (although Talhoffer actually mixes two different styles of 5). Then again, the letters of the alphabet have also changed since that time.