Monthly Measure, designed by Sebastian Bergne, is both a monthly universal calendar and a ruler.
The star can be positioned on the serrated side of the ruler, to show the day of the month and the date. The date can be easily changed by rolling the star along the ruler.
The dates are placed every centimetre so Monthly Measure can also be used as a metric ruler.
The star has English day initials of the week on one side, and French on the other.