Why do equatorial sundials have markings in 15 degree increments? 15 minutes is

Question

Why do equatorial sundials have markings in 15 degree increments?

15 minutes is a quarter of an hour, corresponding to a reasonable time interval.

On average, the sun moves 15 degrees per hour in the sky, so the shadow changes by 15 degrees every hour as well.

The gnoman can be adjusted to point within 15 degrees of the meridian.

15 minutes is a quarter of an hour, corresponding to a reasonable time interval.

On average, the sun moves 15 degrees per hour in the sky, so the shadow changes by 15 degrees every hour as well.

The gnoman can be adjusted to point within 15 degrees of the meridian.

Explanation / Answer

b)On average, the sun moves 15 degrees per hour in the sky, so the shadow changes by 15 degrees every hour as well.

since the earth rotates 15 degrees per hour, the shadow on the sundial should move 15 degrees for every hour.
So these marks that you put on the sundial are just hour marks. If you set up your dial correctly, you should see
that the gnomon will cast its shadow on a new mark every hour.

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