udunits/src/main/java/ucar/units/OffsetUnit.java
public double toDerivedUnit(final double amount) throws ConversionException {
        if (!(_unit instanceof DerivableUnit)) {
            throw new ConversionException(this, getDerivedUnit());
        }
        return ((DerivableUnit) getUnit()).toDerivedUnit(amount + getOffset());
    }
public double toDerivedUnit(final double amount) throws ConversionException {
        if (!(_unit instanceof DerivableUnit)) {
            throw new ConversionException(this, getDerivedUnit());
        }
        return ((DerivableUnit) getUnit()).toDerivedUnit(amount + getOffset());
    }
Converts a value in this unit to the equivalent value in the convertible
derived unit.

@param amount
The value in this unit.
@return The equivalent value in the convertible derived unit.
@throws ConversionException
Can't convert between units.