Two-thirds of this cubit were taken for
The Black foot = 14·186 inches, divided into 16 digits of the 24 digits or qiráts of the cubit.
This cubit and foot are still in use. The old nilometer on the island of Al-Rauzah (Rode) near Cairo has its scale in cubits of this standard, and measurement of the worn scale gives 21·29 inches for the cubit.
The cubit and foot of Al-Mamūn are the basis of measures and of weights which spread from Egypt to every country in Europe.
The story of the five cubits, ancient and medieval, has shown that they were all derived, directly or indirectly, from the meridian measurement of the earth, some of them being probably instituted with the desire to make them representative of the relation of latitude and longitude.
I venture to say that every measure and weight used throughout the world has been developed from one of these cubits and thus, more or less directly, from the Egyptian meridian cubit. The Republican system of France is but a decimal imitation of the system based on the common Egyptian meridian cubit; its basis being the kilometre, 1/10000 of the quarter-meridian, instead of the Egyptian meridian mile, 1/(90 × 60) of the quarter-meridian.
There were some other cubits of minor importance; one of them is the Hashími cubit described in [Chapter XVII].
Comparative Lengths of the Five Ancient Cubits
| Egyptian | common | cubit | = 18·24 | in.; | its foot | 2/3 = 12·16 | in. |
| „ | royal | „ | = 20·64 | „ | „ | 2/3 = 13·76 | „ |
| Great Assyrian | „ | = 25·26 | „ | „ | 1/2 = 12·63 | „ | |
| Beládi | „ | = 21·888 | „ | „ | 1/2 = 10·944 | „ | |
| Black | „ | = 20·28 | „ | „ | 2/3 = 14·186 | „ | |