Convert from mkono [Africa] to button measure

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 (button measure)
The button measure is a unit of distance equal to 1/40 inch (0.635 millimeter), used to measure the thickness of buttons.