anchor.diff:  		end_date :: pos_integer() | undefined,
   		type :: product_price_type() | undefined,
   		period :: recur_period() | undefined,
  -		units :: unit_of_measure() | undefined,
  +		units :: octets | seconds | messages | undefined,
   		size :: integer() | undefined,
   		amount :: integer() | undefined,
   		currency :: string() | undefined,
  
positive.code: 		| active | inactive | terminated.
  -type pla_status() :: created | active | cancelled | terminated.
  -type product_price_type() :: recurring | one_time | usage | tariff.
  -type unit_of_measure() :: octets | cents | seconds | messages.
  -type recur_period() :: hourly | daily | weekly | monthly | yearly.
  
  -record(quantity,
  
negative.code: 		end_date :: pos_integer() | undefined,
  		type :: product_price_type() | undefined,
  		period :: recur_period() | undefined,
  		units :: cents | octets | seconds | messages | undefined,
  		size :: integer() | undefined,
  		amount :: integer() | undefined,
  		currency :: string() | undefined}).
  