#add no longer accepts { quantity: power }. It only accepts nil or { quantty_symbol: power } for qtys argument. Retrieval of unknown quantity raises error. Using ISQ constants to load_isq.
corrected electric_capacitance label
Renaming factor => factors. Factors holds array with polynomial conversion coefficients to base units. Added #derived? method (derived is not base).
#add_prefix just passes args to Prefix #initialize. #add_unit gets quantities from system_of_quantities and passes args to Unit #initialize. Corrected #base_units. Added #derived_units. #load_si using SI unit constants to initialize all units..
corrected expected derived units count
Renaming #equivalent_to? => #same_kind_as? (according to JCGM 200).
using factor, scale instead of array of factors.
Using factor, scale instead of array of factors. Added Comparison, Inspection and Multiplication methods.