public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof NumberTickUnit)) {
            return false;
        }
        if (!super.equals(obj)) {
            return false;
        }
        NumberTickUnit that = (NumberTickUnit) obj;
        if (!this.formatter.equals(that.formatter)) {
            return false;
        }
        return true;