I've saved two rulers with clear crazy glue and sandwich bags. Follow the instructions like moisten both sides of the ruler, and apply glue. You need some place where no one will bother it as it dries. Place the ruler on a plastic bag, and one bag over it. wait twenty-four hours and peel off the plastic. some will stay on, it fuses at the crack, but while there is the line of the crack, you will have a strong transparent seal.