Ink Calender by Oscar Diaz

awesome...

“Ink Calendar” make use the timed pace of the ink spreading on the paper to indicate time.
The ink is absorbed slowly, and the numbers in the calendar are “printed” daily. One a day, they are filled with ink until the end of the month........The “Ink Calendar” was developed for “Gradual “, an exhibition featuring works, which were evolving during the exhibition time at the London Design Festival 2007.

images and more info can be found here