public boolean addCoef(String name, BigDecimal coefficient) {
        if (name != null && !name.equals("") && !this.existInList(name) && coefficient != BigDecimal.ZERO && this.coefficientList != null) {
            Unit unit = new Unit(name, coefficient, false);
            this.coefficientList.add(unit);
            unit.setType(this);
            return true;
        }
        return false;
    }