// len+-
if (minus_ == plus_) {
if (len_.unit() != minus_.unit())
buffer << unit_name[len_.unit()];
buffer << "+-" << minus_.value();
buffer << unit_name[minus_.unit()];
// len+-
if (minus_ == plus_) {
if (len_.unit() != minus_.unit())
buffer << unit_name[len_.unit()];
buffer << "+-" << minus_.value();
buffer << unit_name[minus_.unit()];