# Analog Watch Compass Theory

## Introduction

When we are having outdoor activities, sometimes it is important to know the direction, even without having a compass. There are a couple of ways to determine the direction without a compass. One of the easiest way to determine the direction is to use a watch as a compass in the day time. As we will see later, the rule is extremely simple. However, I could hardly find any theory for the rule explaining why we could do so from the Internet.

In this blog post, I would like to discuss about the analog watch compass and the theory behind it.

## Analog Watch Compass

### Direction Determination

The approximate direction can be determined by comparing the position of the hour hand to the sun. Keep in mind that these determinations are approximate as there is some discrepancy at different latitudes and in different seasons.

Lay the watch horizontally and align the hour hand of the watch with the direction of the sun. The middle point between the alignment of the sun with the hour hand, and the 12 o’clock position on the dial, approximately indicates south.

Positioning the rotating bezel so that it points south, will then allow you to read other approximate compass directions.

### Analog Watch Compass Theories

In the analog watch compass model, we use the reference that the earth is stationary and the sun moves around the earth. We also assume that the time that the sun is closest to the observer on the earth is noon, i.e., 12:00PM without day light saving and 1:00PM with day light saving.

In the northern hemisphere, at noon, when we align the hour hand of the watch with the direction of the sun, the hour hand direction points to south and its opposite points to north.

When the sun starts to move from east to west, in every 2 hours, the sun moves around the earth for $360 / (24 / 2) = 30$ degree, which happens to be equivalent to the degree that the hour hand moves on the watch in 1 hour.

So when we looked at the time, we actually know how many hours it is now before or after noon, and how much degree it is before or after the sun moves to the position that is the closest to the observer, which is at the south direction.

For example, in the top-left figure, it is roughly 10:00AM. We know it is 2 hours before the noon, and the hour hand is pointing to the sun which is 30 degree east to the south direction. Therefore, we could infer the south direction from the current hour hand direction, which is the 11:00 AM direction.

## Conclusion

The details of day light saving is very confusing if we don’t understand the theory. The analog watch trick and its theory might also be useful for your safety in the future.

Lei Mao

07-01-2022

07-01-2022