Convert from mkono [Africa] to shaftment

Unit Definition (mkono [Africa])
The mkono is a traditional unit of distance in East Africa, standardized under British rule as 1/2 yard (18 inches, or 45.72 centimeters). This unit is an African version of the cubit.

Unit Definition (shaftment)
A shaftment, when used as a unit of length, is usually six inches or two palms, i.e. 15.24 cm (for the international inch). It is thought to be the distance from the tip of the outstretched thumb to the other side of the palm.In English this unit has mostly fallen out of use, as do others based on the human arm: digit (1/8 shaftment), finger (7/48 shaftment), palm (½ shaftment) hand (2/3 shaftment), span (1½ shaftments), cubit (3 shaftments) and ell (7½ shaftments).