How it Works
In the example above, Providence, RI is to the east of the middle of the Eastern Time Zone, so solar noon is before 12:00 AM. The longitude of the middle of the Eastern Time Zone is 75 West (5 hours x 15 degrees per hour). Providence is to the east at 71.3 West. The Longitude Offset is 75 - 71.3 = 3.7 degrees to the east. Mean solar noon is 15 minutes before 12:00 AM.
The close-up below shows the scale indicating Longitude Offset degrees on the time zone lens. The black line with the double-ended cross arrow aligns with the white dot on the support post at the ''zero offset' point. From there rotate the lens counterclockwise (east) for east-of-middle locations and clockwise (west) for west-of-middle locations.
The International World Time Clock, and decorative wall desktop clock work differently, click below to learn more about Earthdial™.