How do you mend a broken ruler properly?

To mend a broken ruler properly, clean the broken edges to remove any dust or debris, ensuring a tight fit. Use a strong adhesive, such as super glue or epoxy, to bond the pieces together, applying it evenly along the break. Clamp the ruler securely while the adhesive sets, following the manufacturer's drying time instructions. Once fully cured, you can sand the joint lightly for a smooth finish.