 Now the kilogram is redefined in such a way that the Planck constant is prescribed a value of exactly 

Until 1960, the meter was defined by a platinum-iridium prototype bar with two marks on it (that were, by definition, spaced apart by one meter), the international prototype of the metre, and in 1983 the meter was redefined to be the distance in free space covered by light in 1/299,792,458 of a second (thus "defining" the speed of light to be 299,792,458 meters per second).In many sciences, from pathology to taxonomy, "prototype" refers to a disease, species, etc.which sets a good example for the whole category.