We could build a horizontal sundial on a flat, level base plate and make sure that the shadow stick is angled so that it is parallel to the earth's north-south axis. However, marking the points where the shadow will fall at each hour is not as simple as it might seem. These points change depending on latitude.

At a high northerly latitude the marks would look like this:		But closer to the equator, they would look like this:

As a result, there are two significant drawbacks:

1. Trigonometric calculations are required to work out the hour mark positions - easy to do with a calculator but very tricky without.

2. Even if the hour marks could be calculated the gaps between them would be unequal, making measurement of periods shorter than an hour difficult.

Solving the latitude problem 

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