West Lose Subtract (WLS) is a memory abbreviation which should be kept in mind while finding the time at a longitude when Greenwich time is given. Places on the same meridian have the same local (sun) time. Since the earth makes one complete revolution in 24 hours, it passes through 15 degrees in one hour (360/24 = 15) or 1 degree in 4 minutes. The earth rotates from west to east. Hence places east of Greenwich see the sun earlier and gain time; whereas places west go Greenwich see the sun later and lose time. As such, for places east to Greenwich add 4 minutes to Greenwich time for every degree of longitude, and for places west of Greenwich subtract 4 minutes from Greenwich time for every degree of longitude. A simple memory aid for this will be West Lose Subtract (WLS) and East Gain Add (EGA).