udunits/src/main/java/ucar/units/OffsetUnit.java
@Override
    protected Unit myMultiplyBy(final Unit that) throws MultiplyException {
        return that instanceof OffsetUnit
                ? getUnit().multiplyBy(((OffsetUnit) that).getUnit())
                : getUnit().multiplyBy(that);
    }
@Override
    protected Unit myMultiplyBy(final Unit that) throws MultiplyException {
        return that instanceof OffsetUnit
                ? getUnit().multiplyBy(((OffsetUnit) that).getUnit())
                : getUnit().multiplyBy(that);
    }
Multiply this unit by another unit.

@param that
The unit to multiply this unit by.
@return The product of this unit and <code>that</code>. The offset of
this unit will be ignored; thus, for example
"celsius.myMultiplyBy(day)" is equivalent to
"kelvin.myMultiplyBy(day)".
@throws MultiplyException
Can't multiply these units together.