GMT is known in Aviation radio lingo as “Zulu” time, as opposed to local or “Lima” time. GMT is also known as “Coordinated Universal Time”. There is a short-wave radio station broadcasting out of Ft. Collins, CO, call letters WWV, which does nothing but broadcast the time, which refers to it as Coordinated Universal Time.
Thanks to everyone. I asked the wrong question.
The “GMT-400” never changed in real time. So why is it there?
5.56mm