Ever since we became aware of the concept of time and the fact that it is irreversible and passes by, we continually develop new ways of measuring and visualizing time. Throughout the history of temporal measurement, there have been a variety of devices made to measure time: the sundial, the water clock, the hourglass, and of course, the modern clocks and watches.

Among some of the oddest devices made for measuring time is the *Mengenlehreuhr *(Set Theory Clock) also known as the Berlin Clock. After its construction in 1975, it became the first public clock that uses illumination and color to show time (probably the first digital clock). It is also written down in the Guinness Book of Records.

German watchmaker Dieter Binninger designed the clock under the Commission of the Senate of Berlin. On 17th June 1975, the Berlin Clock was installed at the Kurfürstendamm on the corner with Uhlandstraße, where it remained until 1995 when it was relocated in Budapester Straße in front of Europa-Center, where it can still be seen today.

At first glance, the Berlin Clock looks complicated and confusing but decoding the lights and reading the time is actually really simple. This clock uses a branch of mathematical logic called Set Theory (“Mengenlehreuhr” on German) and combines its principles with light signals to visualize the passage of time.

Structurally speaking, there is a total of 24 lights divided into five rows beginning with a single light at the top whose role is to measure the seconds; this light is followed by two rows that show the hours and two more rows that show the passing of minutes.

The proper way to read the clock is from top to bottom. Here is the formula by which the clock can be read: The row under the single (seconds) light has four red light fields, and each of them is representing an interval of five hours. The next row also has four fields which represent one full hour each. These two “hour” rows together contain the entire 24-hour cycle of a day. The following row has 11 yellow-and-red lights, and every single one of them is showing a five minutes interval. The last row has four more yellow light fields which correspond to one minute each (four lights – four minutes).

If we take the picture above as an example, we can see that the first four fields row has two fields lit (5 x 2 = 10); the second row is turned off, so the hour value is still 10; in the third row we can count six five minute lights that are lit (6 X 5 = 30); the last row has only one light glowing which means that the minutes value is 31. This means that the lights of the Berlin Clock are showing exactly 10:31.

Besides its attractive futuristic design from the 1970s, the clock became even more popular as Berlin’s landmark after part of the message of the famous Kryptos Sculpture was decoded.

When deciphered, part of the text on this sculpture located at the CIA headquarters reads “BERLIN CLOCK.”

Today, many code breakers which are still trying to solve the Kryptos riddle, visit the Berlin Clock hoping that it will help them find the solution.