Decrease time in watch while going from west longitudes to east longitude

When a person travels from west longitudes to east longitude, he moves ahead in time zones. This means that the time at the destination is ahead of the time at the departure point. Hence, the person needs to decrease the time in his watch to match the local time of the destination.

Explanation:

Time zones are determined by the longitudinal lines that divide the Earth's surface into 24 equal parts, each representing one hour of difference in time. The Prime Meridian, which passes through Greenwich in London, is used as the reference point to calculate time zones. The Earth rotates from west to east, and as it does, the Sun appears to move across the sky. This means that as one moves towards the east, the local time at that point increases, and as one moves towards the west, the local time decreases.

For example, if a person travels from New York, which is in the Eastern Time Zone (UTC-5), to London, which is in the Greenwich Mean Time Zone (UTC+0), he needs to adjust his watch by 5 hours behind to match the local time at London. Conversely, if he travels from London to New York, he needs to adjust his watch by 5 hours ahead to match the local time at New York.

Conclusion:

In conclusion, when a person travels from west longitudes to east longitude, he needs to decrease the time in his watch to match the local time at the destination. This adjustment is necessary because the time at the destination is ahead of the time at the departure point due to the Earth's rotation.

But why??... please explain!!