Operating an amateur radio requires quick thinking to change time zones in your head. Many HF net meetings have their gatherings on the air from all over the world.
If the net control person, Kurmanbek, of such a net meeting lives in Bishkek, Kyrgyzstan, he will not announce the meeting using local time saying, “The next meeting will be at 8:15 PM my time,” as it will confuse most of the participants. Honestly, who knows where the country of Kyrgyzstan is? Instead, the meeting time will be announced something like, “The next World Teachers-Who-Are-Hams net meeting will be at 14:15 UTC next Tuesday on this frequency of 14.155. This way, doing my subtraction of 14-6 (I am on the GMT-6 zone) I know that next Tuesday I, Richard, need to be ready at 8:15 AM my local time for the meeting, while the net operator, Kurmanbek, will be at his radio at 8:15 PM his local time, and Tomiko, in Japan, needs to be at her rig at 11:15 PM her local time.
For those of us who are not that adept at arithmetic, here is a handy clock showing the current UTC (Universal Time Coordinate) time, and for my own benefit I added a clock showing my local time.