Standard time on land.

The boundaries of time zones on land generally agree with that at sea, which are defined by the meridians 7½°, 22½°, etc, except when modified as necessary by the territorial limits of the countries concerned. Zone time on land is referred to as standard time. For example, the landmass of South Africa falls into two time zones, namely A and B. For convenience sake it was decided a long time ago that we would use the time in zone B for the entire country. This is referred to as South African Standard Time.

This system allows the same time to be kept whether on land or at sea throughout each zone. The times differ in the various zones by an integral number of hours but the minutes and seconds in all zones remain the same.

Universal Time/Greenwich Mean Time.

Greenwich mean time (GMT) is kept in zone 0 and all zones are adjusted to GMT . For example, the time kept in zone (-8) is 8 hours in advance of GMT while in zone (+8) the time kept is 8 hours slow on that of GMT. To convert the time in any of the zones to GMT, the number of hours given by the zone number (+) or (-) must be added or subtracted from the ship’s zone time.

As previously stated GMT is also known as Universal Time. A table giving the GMT and zone time equivalents as well as the boundaries of each zone can be found at the end of this chapter.