What is a Cubit
A cubit is an ancient measurement of lenght. While the common cubit was the length of the forearm from the elbow to the tip of the middle finger – usually around 45.7 cm, the "royal cubit" was slightly longer: A common cubit plus the width of the palm of the Pharaoh ruling at the time.
At every full moon, the cubit sticks had to be brought to the royal cubit master and compared to it. Failure to do so was punishable by death. With this standardization and uniformity of length, they achieved amazing accuracy.
As an example, the Great Pyramid of Giza is constructed with sides of 440 cubits (230.364 meters). Using cubit sticks, the builders were within 11.4 cm – an accuracy better than 0.05%.
CALIBRATION AND VERIFCATION
The egyptian cubit shaped the first, basic ideas of modern calibration over 4000 years ago, and brought with it a common unit of measurement, traceability, a hierarchy of standards with regular re-calibration intervals.