Certainly! Here are some personalized gift ideas for your wife based on her interests in designing and mathematics, keeping in mind your budget of under $100 and the preference for a small, usable gift for your anniversary: Customized Jewelry: Consider getting a piece of jewelry customized with a design or mathematical symbol that holds significance for both of you. It could be a necklace with a pendant featuring a favorite equation or a bracelet with an engraving of a meaningful mathematical theorem.