         )
     }
 
+    /**
+     Returns hundredweight `[cwt]` mass unit.
+     
+     - author: Michal Konturek
+     */
     public static var hundredweight: MassUnit {
         return MassUnit(
             name: "hundredweight",


extension NSNumber {

    public func ton() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.ton)
    }

    public func hundredweight() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.hundredweight)
    }

    public func quarter() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.quarter)
    }

    public func stone() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.stone)
    }

    public func pound() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.pound)
    }

    public func ounce() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.ounce)
    }

    public func drachm() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.drachm)
    }

    public func grain() -> Quantity {
        return Quantity(amount: self, unit: MassUnit.grain)
    }

        )
    }

    /**
     Returns stone `[st]` mass unit.
     
     - author: Michal Konturek
     */
    public static var stone: MassUnit {
        return MassUnit(
            name: "stone",
