Often see people getting confused when converting their local time into Zulu time, especially when planning or making events.
This link here is a great way to convert your local time into GMT or Zulu time (which is the same.
a little back ground. The world takes 24hrs to turn complete round its axis, this is called a day. Therefore as the world is 360 degrees for every 15 degree segement you travel around the world you will be 1 hr different from the previous one. 360/24 = 15.
In the 1700’s when sailors where exploring the world they could work out their LATITUDE (how far North or South of the Equator) by measuring the angle of the sun when it was at local noon, ie at the highest point of the day. But they could not work out how far ROUND the earth they where until they had made a watch that would not lose time no matter how rough the sea was! However in order to work out how far around the world they where they needed to know the time at a specific point on the earth which the clock on the ship would be set, no matter where on the surface they where.
The p[lace they choose was Greenwich in the UK, just outside London as this is where the Royal Observatory was placed and a lot of the calulations had been made. Therefore when it was noon at Greenwich the clocks set to Greenwish Mean Time (GMT) all over the world also said noon!
To work out your longitude (how far around the earth you where) at Local noon you checked your ships clock and you could work out the difference, either ahead or behind of Noon at Greenwich and with a little bit of Maths you could work out how far around the world you where.
In modern, international times, the name GMT is often changed to UTC (Universal Time Zone, still used by Mariners) or ZULU TIME (which was started by the military and is now used in the world of aviation).