Convert from truss to once [France]

Unit Definition (truss)
The truss is a traditional weight unit, generally equal to 4 stone or 56 pounds (about 25.4 kilograms). The truss was used primarily for measuring hay. In 1795, Parliament specified that a truss of hay should equal 56 pounds for old hay or 60 pounds (about 27.2 kilograms) for new hay.

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).