Time Zones
So with that little story we’ve clearly established that the East Coast is 3 hours ahead of the West Coast. This explains why we get tired so early when visiting our West Coast friends. We want to go to bed when they are all set to go out! Come morning, we wake up a good 3 hours before they do! This also explains why all of us folks from the continental U.S. get up to see dawn in Hawai’i. How many of us would normally get up at dawn during a vacation back home? I suspect not many.

It turns out that this time difference is the key to measuring Longitude. Set your watch at home. Travel someplace. Compare your watch to the local time. The difference between the time back home and the time at your new location will tell you how far East or West you have traveled.

If you travel West, your watch will show a time that is LATER than the local time;
If you travel East, your watch will show a time that is EARLIER than the local time.

Think about it:
If you travel from Baltimore to San Francisco, and don’t reset your watch, what time will your watch say when it is noon in San Francisco (PST)?