The Berlin Clock, also called Set Theory Clock or *Mengenlehre Uhr* (Mengenlehre=Set theory, Uhr=clock in German) is located in Berlin’s busy Europa Center, not far from the famous Kaiser Wilhelm Gedaechtniskirche http://www.walled-in-berlin.com/j-elke/ertle/iconic-kaiser-wilhelm-memorial-church/. The clock, which looks more like a modern sculpture than a timepiece, defies conventional methods of telling time. It tells the time using the Mengenlehre or Set Theory rather than numbers.

### Set Theory and the Berlin Clock

Set theory is a branch of mathematics that deals with the properties of well-defined collections of objects. A set is considered a collection of objects with something in common. That common element might be prime numbers, birds that visit a feeder or the group of colleagues in a department. In other words, a set is a collection of definite, distinguishable objects that can be conceived as a whole. The Russian-born, German mathematician Georg Cantor invented set theory between 1874 and 1884. It has become a fundamental theory in mathematics.

In 1975, the Berlin Senate commissioned inventor and watchmaker, Dieter Binninger, to create the Berlin Clock. The unorthodox timepiece was originally located on the Kurfuerstendamm at the corner of Uhlandstrasse and was moved in 1996 to its present location.

### How the Berlin Clock displays the time

The Berlin Clock uses set theory and a system of colored lights in four rows to display the time in a 24-hour format. The first row contains four fields. Each of these fields represents five hours. The second row holds another four fields. Each of these fields stands for a single hour. In this way, the clock can display a full 24-hour day. http://www.europa-center-berlin.de/en/the-sights/set-theory-clock.html

Each yellow and red field in the third row stands for five minutes. The red fields in the third row represent** **completed quarter-hours (15, 30 and 45 minutes past the hour). In the fourth row, each field represents a single minute. Because the third row consists of eleven fields and the fourth row consists of four fields, a total of 59 minutes can be displayed. It is unnecessary to show 60 minutes because they make a full hour. The round light at the top of the clock blinks every second. Can The current time, therefore, can be determined by sequentially multiplying and adding up the lit fields on the Berlin Clock.

### Can you Read the Time on the Clock in the Photo?

Looking at the photo of the Berlin Clock above, two fields are lit in the top row. Five hours times two equals 10:00, or 10:00 AM. The second row is not lit so that we do not add additional hours. Two fifteen-minute fields are lit in the third row, adding 30 minutes and bringing us to 10:30 AM. A single segment is lit in the fourth row, adding another minute. In other words, the photo was taken at 10:31 AM. Did you get it? Wasn’t that amazing?

For a sneak peek at the first 20+ pages of my memoir, *Walled-In: A West Berlin Girl’s Journey to Freedom*, click “Download a free excerpt” on the home page of http://www.walled-in-berlin.com* Walled-In* is my story of growing up in Berlin during the Cold War.