The clock "block 55M" is intended for measuring the current time in hours and minutes and switching electrical circuits in accordance with a given time program in aviation technology. The clock was installed on one of the blocks of the identification system “6201” (friend or foe) and was intended to automatically switch the identification codes of an aircraft radar interrogator-responder. They have a built-in block of switches and, unlike conventional watches, a 24-hour dial to eliminate double operation per day. The scales and hands are covered with phosphor.