January 21 - Two sticks and a length of string

The great pyramid in Egypt is a most remarkable feat of engineering and technological skill. To make sure that the foundations were absolutely level the builders used an extensive system of water-filled trenches around the base of the pyramid. A string was stretched between two sticks of equal length, held touching the water. The floor of the trench was then leveled until measuring rods showed that the string was parallel with the water level, and the bottom of the trench. This method was so successful that modern experts, with the aid of the most advanced equipment, have found that the north-east corner of the pyramid is only half an inch lower than the south-east corner.

Here's the page -

By the way, I've been using the Macquarie History of Ideas, produced by the Macquarie Library in Australia, so some of the descriptions for things have been taken from it. Other references are from Wikipedia and random websites.