To use the top chart - example: If it's 2:58PM in the
summer then look at the center column up to 2p, and then to the left
(Daylight Savings Time column), and change 1900 to 1958, or if needed change
the 7p to 7:58pm. The 1958 could be expressed as 1958 UTC (UTC has replaced
the term GMT, but GMT is still used), or as Zulu, Z, or Universal Time. If
seconds (59 for example) also need to be displayed then add colons, such as
If there were no minutes then 2:00PM CST could be expressed as Nineteen Hundred Hours.
2400 and 0000 represent exact midnight and are somewhat interchangeable. If you are trying to express time up to midnight then 2359 or 2400 would be a good choice, to express a morning event then starting with 0000, or 0001 would be a good choice.
Some amateur radio contests/events may effectively use both and operate from 0000 to 2400. Stretching out UTC wouldn't be proper - but you may find a bar open to 2600 hours.
Most of the time UTC is referenced and display in hundred hours. The AM PM in the chart is listed just as an alternate to the same UTC time (has no relation to the local time in London, which could be different).
To avoid using this chart then remember "CAST" (Central Add Six for UTC-Time), so add 6 to the current winter CST 24-hour time, if it's 5PM which is 17:00 local then add 6 which is 2300 UTC. During Daylight Savings Time only add 5 which would be 2200 UTC.
To decipher UTC back to Central Standard Time then do the reverse and subtract 6 (5 if DST) from 2300 which is 1700 which would 5PM.
One issue that occurs is as earth spins and it becomes the start of a new day at midnight (1201AM, 0001) on Wednesday in London (Prime Meridian Line), it will still be Tuesday in Dallas for the next 5 or 6 hours till the earth's spin catches up.
So an example of this would be if a meeting is scheduled in advance for Dallas at Tuesday at 8:00PM CST - then that same meeting would also be at Wednesday 0200 UTC (2:00AM). This can be visualized on the circle chart above. The CST has a six hour period from 6PM to Midnight where the UTC date will be on the next day.
One other side of the Prime Meridian Line the example would be backwards, a 2:00 AM local time Sunday meeting in Bangladesh (+6 hrs) would be on Saturday at 2000 UTC time (8PM UTC).
Download the rectangle chart in PDF form: 5 inch tall 6 inch 7 inch 8 inch
Download (save target as) the circle chart HERE , resize if needed.
The ◄ Left & Right ► arrows
change the time zone.