Mengenlehreuhr

After the Senate decommissioned it in 1995, the clock was relocated to a site in Budapester Straße in front of Europa-Center, where it stands today.

• Illustration — Clock displaying time from 16:50 to 17:05 (4:50 pm to 5:05 pm) in time lapse. The Mengenlehreuhr clock face utilizes 24 light fields (1+4+4+11+4=24) to display time in 0–23 hour, 0–59 minute and even/odd second. The clock is read from the top row to the bottom. Second: The top big circular light is the seconds mark. This light switches its state (between ON and OFF) every one second. The light is OFF for even seconds, and ON for odd seconds. On this clock, the precise time in seconds (e.g., 42 in 10:31:42) is not displayed. Rather, this light serves as an indicator that the clock is operating. Second encoder in Source Code Assuming neon[3] holds 1-bit for the 1 second light if(tsec&1){ neon[3]=1; } else{ neon[3]=0; } Hour: The next two rows of 8 red light fields indicate the hour, using a 24-hour format. Each light in the upper row marks 5 full hours, while each light in the lower row marks 1 full hour. Thus, the maximum hour number which can be displayed is 4*5+4=24, and the minimal displayable hour is 0, indicated when all 8 of these lights are OFF. Since a 24-hour clock only uses hour numbers from 0 to 23, an hour number of "24" (the state with all lights ON) is never displayed. Hour encoder in Source Code Assuming neon[0] holds 8-bit for the top 8 lights Hour-top for(uint8_t i=0; i Time decoding - How to Read the Clock== • Illustration — Mengenlehreuhr clock recreation using high voltage neon lamps with clock displaying 12:32:x1 This section demonstrates telling the time, using the accompanying image as an example, in which a time of 12:32 is indicated. Hour (upper row 2 lit, and lower row 2 lit): 2*5+2=12. Each of the 4 upper row lights represents a 5 increment hour: 5, 10, 15, 20. Minute (upper row 6 lit and lower row 2 lit): 6*5+2=32. Each of the 11 upper row lights represents a 5 increment minute: 5,10,15,20,25,30,35,40,45,50,55. Second (top 1): The lamp is lit, indicating an odd number of seconds.

This clock may be referred to in the unsolved section of Kryptos, a sculpture at the Central Intelligence Agency (CIA) headquarters in Langley, Virginia, United States. The sculptor, Jim Sanborn, gave two clues to The New York Times in November 2010 and November 2014, revealing that the portion of the deciphered "K4" sculpture text, in positions 64–74, reads "BERLIN CLOCK". When asked if the clue referred to the Mengenlehreuhr, Sanborn replied, "You'd better delve into that particular clock". However, Sanborn also noted that, "There are several really interesting clocks in Berlin."