Convert from once [France] to as, ass [Northern Europe]

Unit Definition (once [France])
The onça, once, oncia, onza is traditional names for the ounce unit in Romance languages. The French once equals 1/16 livre or about 30.59 grams (1.079 ounce).

Unit Definition (as, ass [Northern Europe])
The as, ass [Northern Europe] is a traditional unit of mass for gold and silver, used in most of northern Europe but not in England. The unit varied in size from about 48 to 58 milligrams (0.75 to 0.90 English grain).