Universal Ring Dial


Figure 56: Universal ring dial

This type of portable dial is called universal because it is adjustable for use in any latitude. Pivoted across the center of the outer ring is a thin metal "bridge". The bridge is slotted and bears a cursor pierced with a tiny hole. The cursor is moved to that point on the bridge which corresponds to the day of the observation. The Sun shining through the tiny hole casts a beam of light on the inner surface of the time ring, which is calibrated to show the hours of the day.

To use the dial, adjust the suspension ring to the correct latitude, using the upper scale if one is at the northern hemisphere and the lower scale if one is at the southern hemisphere. Next, slide the cursor on the bridge to the correct date. Then, put the hour ring 90 down until it touches the stoppers. Then hold the sundial on the string and turn it slowly until a sun ray hits the notch on the hour ring. Now you can tell the local time. If applied correctly, the outer ring will now be aligned in the north-south direction, the hour ring will be parallel to the equator and the bridge with the cursor will be parallel to the axis of the earth.